From 46ac4c271b7afff41969280f8e6419468aeadeaf Mon Sep 17 00:00:00 2001
From: Xie Yuheng <xyheme@gmail.com>
Date: Sun, 28 Apr 2024 15:34:44 +0800
Subject: [PATCH] rename clause keyword to relation

---
 TODO.md                                       |  2 +
 .../tests/finite-domain/FiniteDomain.ch       |  0
 .../finite-domain/FiniteDomain.example.ch     |  0
 .../finite-domain/FiniteDomain.example.ch.out |  0
 .../tests/finite-domain/FiniteDomain.test.ch  |  0
 .../finite-domain/FiniteDomain.test.ch.out    |  0
 .../archive}/tests/finite-domain/index.ch     |  0
 {archive => docs/archive}/tests/hyperrule.ch  |  0
 .../archive}/tests/hyperrule.ch.out           |  0
 .../archive}/tests/hyperrule/abc.ch           |  0
 .../archive}/tests/hyperrule/abc.ch.out       |  0
 .../tests/hyperrule/propagate-idempotent.ch   |  0
 .../hyperrule/propagate-idempotent.ch.out     |  0
 .../hyperrule/propagate-keep-the-input.ch     |  0
 .../hyperrule/propagate-keep-the-input.ch.out |  0
 .../archive}/tests/hyperrule/walk.ch          |  0
 .../archive}/tests/hyperrule/walk.ch.out      |  0
 .../weather-hyperrule-list-as-exp.ch          |  0
 .../weather-hyperrule-list-as-exp.ch.out      |  0
 .../tests/hyperrule/weather-include.ch        |  0
 .../tests/hyperrule/weather-include.ch.out    |  0
 .../tests/hyperrule/weather-with-guard.ch     |  0
 .../tests/hyperrule/weather-with-guard.ch.out |  0
 .../archive}/tests/hyperrule/weather.ch       |  0
 .../archive}/tests/hyperrule/weather.ch.out   |  0
 {archive => docs/archive}/tests/rule.ch       |  0
 {archive => docs/archive}/tests/rule.ch.out   |  0
 .../archive}/tests/rule/arithmetic.ch         |  0
 .../archive}/tests/rule/arithmetic.ch.out     |  0
 .../archive}/tests/rule/combinatory-logic.ch  |  0
 .../tests/rule/combinatory-logic.ch.out       |  0
 .../tests/rule/conjunctive-normal-form.ch     |  0
 .../tests/rule/conjunctive-normal-form.ch.out |  0
 .../archive}/tests/rule/rule-list-as-exp.ch   |  0
 .../tests/rule/rule-list-as-exp.ch.out        |  0
 .../tests/rule/same-pattern-variable.ch       |  0
 .../tests/rule/same-pattern-variable.ch.out   |  0
 .../archive}/tests/rule/with-guard.ch         |  0
 .../archive}/tests/rule/with-guard.ch.out     |  0
 .../archive}/tests/rule/with-include.ch       |  0
 .../archive}/tests/rule/with-include.ch.out   |  0
 .../03-affordable-journeys.ch                 | 37 --------
 .../04-acyclic-directed-graph.ch              | 31 -------
 .../books/clause-and-effect/01-party-pairs.ch | 10 +--
 .../clause-and-effect/01-party-pairs.ch.out   |  0
 .../clause-and-effect/02-drinking-pairs.ch    | 14 ++--
 .../02-drinking-pairs.ch.out                  |  0
 .../03-affordable-journeys.ch                 | 37 ++++++++
 .../03-affordable-journeys.ch.out             |  0
 .../04-acyclic-directed-graph.ch              | 31 +++++++
 .../04-acyclic-directed-graph.ch.out          |  0
 .../books/clause-and-effect/05-member.ch      |  4 +-
 .../books/clause-and-effect/05-member.ch.out  |  0
 .../clause-and-effect/06-length-of-a-list.ch  |  4 +-
 .../clause-and-effect/08-maximum-of-a-list.ch |  6 +-
 .../09-searching-a-cyclic-graph.ch            | 30 +++----
 .../09-searching-a-cyclic-graph.ch.out        |  0
 .../a-boston-high-tech-company.ch             | 84 +++++++++----------
 .../a-boston-high-tech-company.ch.out         |  0
 .../logic-as-programs.md                      | 12 +--
 .../the-reasoned-schemer/01-playthings.ch     |  8 +-
 .../the-reasoned-schemer/01-playthings.ch.out |  0
 .../02-teaching-old-toys-new-tricks.ch        | 16 ++--
 .../02-teaching-old-toys-new-tricks.ch.out    |  0
 .../03-seeing-old-friends-in-new-ways.ch      | 26 +++---
 .../03-seeing-old-friends-in-new-ways.ch.out  |  0
 .../04-double-your-fun.ch                     |  8 +-
 .../04-double-your-fun.ch.out                 |  0
 .../the-reasoned-schemer/05-members-only.ch   | 10 +--
 .../05-members-only.ch.out                    |  0
 .../06-the-fun-never-ends.ch                  |  6 +-
 .../06-the-fun-never-ends.ch.out              |  0
 .../the-reasoned-schemer/07-a-bit-too-much.ch | 54 ++++++------
 .../07-a-bit-too-much.ch.out                  |  0
 .../08-just-a-bit-more.ch                     | 28 +++----
 .../08-just-a-bit-more.ch.out                 |  0
 .../books/the-reasoned-schemer/09-thin-ice.ch |  0
 .../the-reasoned-schemer/10-under-the-hood.ch |  0
 docs/{ => examples}/langs/lambda-closure.ch   | 22 ++---
 .../langs/lambda-closure.ch.out               |  0
 .../langs/lambda-simple-type.ch               | 24 +++---
 .../langs/lambda-simple-type.ch.out           |  0
 docs/examples/std/list/Append.ch              |  6 ++
 docs/{ => examples}/std/list/Append.test.ch   |  0
 .../std/list/Append.test.ch.out               |  0
 docs/{ => examples}/std/list/Lookup.ch        |  4 +-
 docs/{ => examples}/std/list/Lookup.test.ch   |  0
 .../std/list/Lookup.test.ch.out               |  0
 docs/{ => examples}/std/list/index.ch         |  0
 docs/{ => examples}/std/nat/Add.ch            |  4 +-
 docs/{ => examples}/std/nat/Add.test.ch       |  0
 docs/{ => examples}/std/nat/Add.test.ch.out   |  0
 docs/{ => examples}/std/nat/Mul.ch            |  6 +-
 docs/{ => examples}/std/nat/Mul.test.ch       |  0
 docs/{ => examples}/std/nat/Mul.test.ch.out   |  0
 docs/examples/std/nat/Nat.ch                  |  7 ++
 docs/{ => examples}/std/nat/index.ch          |  0
 docs/examples/std/nat/numbers.ch              | 14 ++++
 docs/{ => examples}/std/nat/play.ch           |  2 +-
 docs/{ => examples}/std/nat/play.ch.out       |  0
 docs/examples/std/trilean/Trilean.ch          | 62 ++++++++++++++
 .../{ => examples}/std/trilean/Trilean.ch.out |  0
 .../tests/basic/assert-false.error.ch         |  0
 .../tests/basic/assert-false.error.ch.err     |  0
 .../tests/basic/assert-non-boolean.error.ch   |  0
 .../basic/assert-non-boolean.error.ch.err     |  0
 docs/{ => examples}/tests/basic/assert.ch     |  0
 docs/{ => examples}/tests/basic/compute.ch    |  0
 .../{ => examples}/tests/basic/compute.ch.out |  0
 docs/{ => examples}/tests/basic/currying.ch   |  0
 .../tests/basic/currying.ch.out               |  0
 docs/{ => examples}/tests/basic/dot.ch        |  0
 .../tests/basic/function-print.ch             |  0
 .../tests/basic/function-print.ch.out         |  0
 .../tests/basic/function-with-clause.ch       |  2 +-
 .../tests/basic/function-with-clause.ch.out   |  0
 .../tests/basic/function-with-early-return.ch |  0
 .../basic/function-with-early-return.ch.out   |  0
 .../basic/function-with-return-expression.ch  |  0
 .../function-with-return-expression.ch.out    |  0
 .../tests/basic/function-with-return-null.ch  |  0
 .../basic/function-with-return-null.ch.out    |  0
 docs/{ => examples}/tests/basic/function.ch   |  0
 .../tests/basic/function.ch.out               |  0
 docs/{ => examples}/tests/basic/if-else-if.ch |  0
 .../tests/basic/if-else-if.ch.out             |  0
 .../tests/basic/if-exp-without-else.ch        |  0
 .../tests/basic/if-exp-without-else.ch.out    |  0
 docs/{ => examples}/tests/basic/if-exp.ch     |  0
 docs/{ => examples}/tests/basic/if-exp.ch.out |  0
 .../basic/if-non-boolean-target.error.ch      |  0
 .../basic/if-non-boolean-target.error.ch.err  |  0
 .../tests/basic/if-without-else.ch            |  0
 .../tests/basic/if-without-else.ch.out        |  0
 docs/{ => examples}/tests/basic/if.ch         |  0
 docs/{ => examples}/tests/basic/if.ch.out     |  0
 docs/{ => examples}/tests/basic/let.ch        |  0
 docs/{ => examples}/tests/basic/print.ch      |  0
 docs/{ => examples}/tests/basic/print.ch.out  |  0
 .../tests/constraints/not-equal.ch            |  0
 .../tests/constraints/not-equal.ch.out        |  0
 .../tests/constraints/number-types.ch         |  0
 .../tests/constraints/number-types.ch.out     |  0
 .../tests/constraints/string-types.ch         |  0
 .../tests/constraints/string-types.ch.out     |  0
 .../no-misused-variable-name.error.ch         |  2 +-
 .../no-misused-variable-name.error.ch.err     |  2 +-
 .../no-unused-variable-name.error.ch          |  2 +-
 .../no-unused-variable-name.error.ch.err      |  2 +-
 ...variable-name-can-starts-with-uppercase.ch |  0
 ...able-name-can-starts-with-uppercase.ch.out |  0
 .../conventions/preserved-name-false.error.ch |  0
 .../preserved-name-false.error.ch.err         |  0
 .../conventions/preserved-name-null.error.ch  |  0
 .../preserved-name-null.error.ch.err          |  0
 .../conventions/preserved-name-true.error.ch  |  0
 .../preserved-name-true.error.ch.err          |  0
 .../relation-arity-mismatch.error.ch          |  2 +
 .../relation-arity-mismatch.error.ch.err      |  0
 ...n-name-must-starts-with-uppercase.error.ch |  1 +
 ...me-must-starts-with-uppercase.error.ch.err | 14 ++++
 docs/{ => examples}/tests/globals/boolean.ch  |  0
 .../tests/globals/boolean.ch.out              |  0
 docs/{ => examples}/tests/globals/equal.ch    |  0
 .../{ => examples}/tests/globals/equal.ch.out |  0
 .../{ => examples}/tests/globals/not-equal.ch |  0
 .../tests/globals/not-equal.ch.out            |  0
 .../tests/globals/null-shadowed.ch            |  2 +-
 .../tests/globals/null-shadowed.ch.out        |  0
 docs/{ => examples}/tests/globals/null.ch     |  0
 docs/{ => examples}/tests/globals/null.ch.out |  0
 .../goal-apply-too-many-arguments.error.ch    |  0
 ...goal-apply-too-many-arguments.error.ch.err |  0
 docs/{ => examples}/tests/goal/goal.ch        |  0
 docs/{ => examples}/tests/goal/goal.ch.out    |  0
 docs/{ => examples}/tests/json/array.ch       |  0
 docs/{ => examples}/tests/json/array.ch.out   |  0
 docs/{ => examples}/tests/json/boolean.ch     |  0
 docs/{ => examples}/tests/json/boolean.ch.out |  0
 docs/{ => examples}/tests/json/null.ch        |  0
 docs/{ => examples}/tests/json/null.ch.out    |  0
 docs/{ => examples}/tests/json/number.ch      |  0
 docs/{ => examples}/tests/json/number.ch.out  |  0
 docs/{ => examples}/tests/json/object.ch      |  0
 docs/{ => examples}/tests/json/object.ch.out  |  0
 docs/{ => examples}/tests/json/string.ch      |  0
 docs/{ => examples}/tests/json/string.ch.out  |  0
 docs/{ => examples}/tests/module/A.ch         |  2 +-
 docs/{ => examples}/tests/module/A.ch.out     |  0
 docs/{ => examples}/tests/module/AB.ch        |  2 +-
 docs/{ => examples}/tests/module/AB.ch.out    |  0
 docs/{ => examples}/tests/module/ABC.ch       |  2 +-
 docs/{ => examples}/tests/module/ABC.ch.out   |  0
 docs/examples/tests/module/example.ch         |  5 ++
 .../tests/module/import-all-as.ch             |  0
 .../tests/module/import-all-as.ch.out         |  0
 .../tests/module/import-all-private.error.ch  |  0
 .../module/import-all-private.error.ch.err    |  0
 .../{ => examples}/tests/module/import-all.ch |  0
 .../tests/module/import-all.ch.out            |  0
 .../tests/module/import-private.error.ch      |  0
 .../tests/module/import-private.error.ch.err  |  0
 .../module/imported-name-can-be-shadowed.ch   |  2 +-
 .../imported-name-can-be-shadowed.ch.out      |  0
 .../object/construct-object-by-relation.ch    |  2 +-
 .../construct-object-by-relation.ch.out       |  0
 .../object/merge-properties-to-object.ch      |  0
 .../object/merge-properties-to-object.ch.out  |  0
 docs/{ => examples}/tests/relation/conj.ch    |  0
 .../{ => examples}/tests/relation/conj.ch.out |  0
 docs/examples/tests/relation/datom.ch         |  9 ++
 .../tests/relation/datom.ch.out               |  0
 docs/{ => examples}/tests/relation/disj.ch    |  0
 .../{ => examples}/tests/relation/disj.ch.out |  0
 .../tests/relation/lookup-inline-disj.ch      |  6 +-
 .../tests/relation/lookup-inline-disj.ch.out  |  0
 .../tests/relation/multiset-arithmetic.ch     | 48 +++++------
 .../tests/relation/multiset-arithmetic.ch.out |  0
 .../tests/relation/sat-clause.ch              | 34 ++++----
 .../tests/relation/sat-clause.ch.out          |  0
 .../relation/sequencing-of-procedure-calls.ch | 35 ++++++++
 .../sequencing-of-procedure-calls.ch.out      |  0
 docs/{ => examples}/tests/term/my-list.ch     |  4 +-
 docs/{ => examples}/tests/term/my-list.ch.out |  0
 .../tests/termination/always.ch               |  4 +-
 .../tests/termination/always.ch.out           |  0
 .../tests/termination/append.ch               |  8 +-
 .../tests/termination/append.ch.out           |  0
 docs/examples/tests/termination/never.ch      | 23 +++++
 .../tests/termination/never.ch.out            |  0
 .../tests/unification/infix-notation-equal.ch |  0
 .../unification/infix-notation-equal.ch.out   |  0
 .../unification/infix-notation-not-equal.ch   |  0
 .../infix-notation-not-equal.ch.out           |  0
 .../tests/unification/occur-check.ch          |  0
 .../tests/unification/occur-check.ch.out      |  0
 docs/std/list/Append.ch                       |  6 --
 docs/std/nat/Nat.ch                           |  7 --
 docs/std/nat/numbers.ch                       | 14 ----
 docs/std/trilean/Trilean.ch                   | 62 --------------
 .../relation-arity-mismatch.error.ch          |  2 -
 ...n-name-must-starts-with-uppercase.error.ch |  1 -
 ...me-must-starts-with-uppercase.error.ch.err | 14 ----
 docs/tests/module/example.ch                  |  5 --
 docs/tests/relation/datom.ch                  |  9 --
 .../relation/sequencing-of-procedure-calls.ch | 35 --------
 docs/tests/termination/never.ch               | 23 -----
 src/lang/globals/aboutBoolean.ts              |  4 +-
 src/lang/globals/aboutNull.ts                 |  2 +-
 src/lang/syntax/grammars/stmt.ts              |  8 +-
 src/test.ts                                   |  4 +-
 251 files changed, 511 insertions(+), 509 deletions(-)
 rename {archive => docs/archive}/tests/finite-domain/FiniteDomain.ch (100%)
 rename {archive => docs/archive}/tests/finite-domain/FiniteDomain.example.ch (100%)
 rename {archive => docs/archive}/tests/finite-domain/FiniteDomain.example.ch.out (100%)
 rename {archive => docs/archive}/tests/finite-domain/FiniteDomain.test.ch (100%)
 rename {archive => docs/archive}/tests/finite-domain/FiniteDomain.test.ch.out (100%)
 rename {archive => docs/archive}/tests/finite-domain/index.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/abc.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/abc.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/propagate-idempotent.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/propagate-idempotent.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/propagate-keep-the-input.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/propagate-keep-the-input.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/walk.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/walk.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather-hyperrule-list-as-exp.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather-hyperrule-list-as-exp.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather-include.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather-include.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather-with-guard.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather-with-guard.ch.out (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather.ch (100%)
 rename {archive => docs/archive}/tests/hyperrule/weather.ch.out (100%)
 rename {archive => docs/archive}/tests/rule.ch (100%)
 rename {archive => docs/archive}/tests/rule.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/arithmetic.ch (100%)
 rename {archive => docs/archive}/tests/rule/arithmetic.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/combinatory-logic.ch (100%)
 rename {archive => docs/archive}/tests/rule/combinatory-logic.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/conjunctive-normal-form.ch (100%)
 rename {archive => docs/archive}/tests/rule/conjunctive-normal-form.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/rule-list-as-exp.ch (100%)
 rename {archive => docs/archive}/tests/rule/rule-list-as-exp.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/same-pattern-variable.ch (100%)
 rename {archive => docs/archive}/tests/rule/same-pattern-variable.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/with-guard.ch (100%)
 rename {archive => docs/archive}/tests/rule/with-guard.ch.out (100%)
 rename {archive => docs/archive}/tests/rule/with-include.ch (100%)
 rename {archive => docs/archive}/tests/rule/with-include.ch.out (100%)
 delete mode 100644 docs/books/clause-and-effect/03-affordable-journeys.ch
 delete mode 100644 docs/books/clause-and-effect/04-acyclic-directed-graph.ch
 rename docs/{ => examples}/books/clause-and-effect/01-party-pairs.ch (73%)
 rename docs/{ => examples}/books/clause-and-effect/01-party-pairs.ch.out (100%)
 rename docs/{ => examples}/books/clause-and-effect/02-drinking-pairs.ch (52%)
 rename docs/{ => examples}/books/clause-and-effect/02-drinking-pairs.ch.out (100%)
 create mode 100644 docs/examples/books/clause-and-effect/03-affordable-journeys.ch
 rename docs/{ => examples}/books/clause-and-effect/03-affordable-journeys.ch.out (100%)
 create mode 100644 docs/examples/books/clause-and-effect/04-acyclic-directed-graph.ch
 rename docs/{ => examples}/books/clause-and-effect/04-acyclic-directed-graph.ch.out (100%)
 rename docs/{ => examples}/books/clause-and-effect/05-member.ch (80%)
 rename docs/{ => examples}/books/clause-and-effect/05-member.ch.out (100%)
 rename docs/{ => examples}/books/clause-and-effect/06-length-of-a-list.ch (86%)
 rename docs/{ => examples}/books/clause-and-effect/08-maximum-of-a-list.ch (79%)
 rename docs/{ => examples}/books/clause-and-effect/09-searching-a-cyclic-graph.ch (61%)
 rename docs/{ => examples}/books/clause-and-effect/09-searching-a-cyclic-graph.ch.out (100%)
 rename docs/{ => examples}/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch (87%)
 rename docs/{ => examples}/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch.out (100%)
 rename docs/{ => examples}/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md (92%)
 rename docs/{ => examples}/books/the-reasoned-schemer/01-playthings.ch (93%)
 rename docs/{ => examples}/books/the-reasoned-schemer/01-playthings.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch (91%)
 rename docs/{ => examples}/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch (87%)
 rename docs/{ => examples}/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/04-double-your-fun.ch (93%)
 rename docs/{ => examples}/books/the-reasoned-schemer/04-double-your-fun.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/05-members-only.ch (93%)
 rename docs/{ => examples}/books/the-reasoned-schemer/05-members-only.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/06-the-fun-never-ends.ch (93%)
 rename docs/{ => examples}/books/the-reasoned-schemer/06-the-fun-never-ends.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/07-a-bit-too-much.ch (73%)
 rename docs/{ => examples}/books/the-reasoned-schemer/07-a-bit-too-much.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/08-just-a-bit-more.ch (63%)
 rename docs/{ => examples}/books/the-reasoned-schemer/08-just-a-bit-more.ch.out (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/09-thin-ice.ch (100%)
 rename docs/{ => examples}/books/the-reasoned-schemer/10-under-the-hood.ch (100%)
 rename docs/{ => examples}/langs/lambda-closure.ch (57%)
 rename docs/{ => examples}/langs/lambda-closure.ch.out (100%)
 rename docs/{ => examples}/langs/lambda-simple-type.ch (58%)
 rename docs/{ => examples}/langs/lambda-simple-type.ch.out (100%)
 create mode 100644 docs/examples/std/list/Append.ch
 rename docs/{ => examples}/std/list/Append.test.ch (100%)
 rename docs/{ => examples}/std/list/Append.test.ch.out (100%)
 rename docs/{ => examples}/std/list/Lookup.ch (79%)
 rename docs/{ => examples}/std/list/Lookup.test.ch (100%)
 rename docs/{ => examples}/std/list/Lookup.test.ch.out (100%)
 rename docs/{ => examples}/std/list/index.ch (100%)
 rename docs/{ => examples}/std/nat/Add.ch (57%)
 rename docs/{ => examples}/std/nat/Add.test.ch (100%)
 rename docs/{ => examples}/std/nat/Add.test.ch.out (100%)
 rename docs/{ => examples}/std/nat/Mul.ch (82%)
 rename docs/{ => examples}/std/nat/Mul.test.ch (100%)
 rename docs/{ => examples}/std/nat/Mul.test.ch.out (100%)
 create mode 100644 docs/examples/std/nat/Nat.ch
 rename docs/{ => examples}/std/nat/index.ch (100%)
 create mode 100644 docs/examples/std/nat/numbers.ch
 rename docs/{ => examples}/std/nat/play.ch (94%)
 rename docs/{ => examples}/std/nat/play.ch.out (100%)
 create mode 100644 docs/examples/std/trilean/Trilean.ch
 rename docs/{ => examples}/std/trilean/Trilean.ch.out (100%)
 rename docs/{ => examples}/tests/basic/assert-false.error.ch (100%)
 rename docs/{ => examples}/tests/basic/assert-false.error.ch.err (100%)
 rename docs/{ => examples}/tests/basic/assert-non-boolean.error.ch (100%)
 rename docs/{ => examples}/tests/basic/assert-non-boolean.error.ch.err (100%)
 rename docs/{ => examples}/tests/basic/assert.ch (100%)
 rename docs/{ => examples}/tests/basic/compute.ch (100%)
 rename docs/{ => examples}/tests/basic/compute.ch.out (100%)
 rename docs/{ => examples}/tests/basic/currying.ch (100%)
 rename docs/{ => examples}/tests/basic/currying.ch.out (100%)
 rename docs/{ => examples}/tests/basic/dot.ch (100%)
 rename docs/{ => examples}/tests/basic/function-print.ch (100%)
 rename docs/{ => examples}/tests/basic/function-print.ch.out (100%)
 rename docs/{ => examples}/tests/basic/function-with-clause.ch (91%)
 rename docs/{ => examples}/tests/basic/function-with-clause.ch.out (100%)
 rename docs/{ => examples}/tests/basic/function-with-early-return.ch (100%)
 rename docs/{ => examples}/tests/basic/function-with-early-return.ch.out (100%)
 rename docs/{ => examples}/tests/basic/function-with-return-expression.ch (100%)
 rename docs/{ => examples}/tests/basic/function-with-return-expression.ch.out (100%)
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diff --git a/TODO.md b/TODO.md
index ceec60d6..d6b7a35a 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,3 +1,5 @@
+用 constraint programming 的知识来实现类型检查器。
+
 `Data` instead of `Term` -- only defined by `datatype`
 
 [maybe] remove eval
diff --git a/archive/tests/finite-domain/FiniteDomain.ch b/docs/archive/tests/finite-domain/FiniteDomain.ch
similarity index 100%
rename from archive/tests/finite-domain/FiniteDomain.ch
rename to docs/archive/tests/finite-domain/FiniteDomain.ch
diff --git a/archive/tests/finite-domain/FiniteDomain.example.ch b/docs/archive/tests/finite-domain/FiniteDomain.example.ch
similarity index 100%
rename from archive/tests/finite-domain/FiniteDomain.example.ch
rename to docs/archive/tests/finite-domain/FiniteDomain.example.ch
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rename to docs/archive/tests/finite-domain/FiniteDomain.example.ch.out
diff --git a/archive/tests/finite-domain/FiniteDomain.test.ch b/docs/archive/tests/finite-domain/FiniteDomain.test.ch
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similarity index 100%
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diff --git a/archive/tests/rule/same-pattern-variable.ch b/docs/archive/tests/rule/same-pattern-variable.ch
similarity index 100%
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rename to docs/archive/tests/rule/same-pattern-variable.ch
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similarity index 100%
rename from archive/tests/rule/same-pattern-variable.ch.out
rename to docs/archive/tests/rule/same-pattern-variable.ch.out
diff --git a/archive/tests/rule/with-guard.ch b/docs/archive/tests/rule/with-guard.ch
similarity index 100%
rename from archive/tests/rule/with-guard.ch
rename to docs/archive/tests/rule/with-guard.ch
diff --git a/archive/tests/rule/with-guard.ch.out b/docs/archive/tests/rule/with-guard.ch.out
similarity index 100%
rename from archive/tests/rule/with-guard.ch.out
rename to docs/archive/tests/rule/with-guard.ch.out
diff --git a/archive/tests/rule/with-include.ch b/docs/archive/tests/rule/with-include.ch
similarity index 100%
rename from archive/tests/rule/with-include.ch
rename to docs/archive/tests/rule/with-include.ch
diff --git a/archive/tests/rule/with-include.ch.out b/docs/archive/tests/rule/with-include.ch.out
similarity index 100%
rename from archive/tests/rule/with-include.ch.out
rename to docs/archive/tests/rule/with-include.ch.out
diff --git a/docs/books/clause-and-effect/03-affordable-journeys.ch b/docs/books/clause-and-effect/03-affordable-journeys.ch
deleted file mode 100644
index b92cad06..00000000
--- a/docs/books/clause-and-effect/03-affordable-journeys.ch
+++ /dev/null
@@ -1,37 +0,0 @@
-clause Border("sussex", "kent")
-clause Border("sussex", "surrey")
-clause Border("surrey", "kent")
-clause Border("hampshire", "sussex")
-clause Border("hampshire", "surrey")
-clause Border("hampshire", "berkshire")
-clause Border("berkshire", "surrey")
-clause Border("wiltshire", "hampshire")
-clause Border("wiltshire", "berkshire")
-
-clause Adjacent(x, y)
----------------- border {
-  Border(x, y)
-}
-
-clause Adjacent(x, y)
----------------- symmetry {
-  Border(y, x)
-}
-
-clause Affordable(x, y)
--------------------- {
-  Adjacent(x, z)
-  Adjacent(z, y)
-}
-
-print find to_kent {
-  Affordable(to_kent, "kent")
-}
-
-print find to_sussex {
-  Affordable("sussex", to_sussex)
-}
-
-print find [x, y] {
-  Affordable(x, y)
-}
diff --git a/docs/books/clause-and-effect/04-acyclic-directed-graph.ch b/docs/books/clause-and-effect/04-acyclic-directed-graph.ch
deleted file mode 100644
index 64c70cfd..00000000
--- a/docs/books/clause-and-effect/04-acyclic-directed-graph.ch
+++ /dev/null
@@ -1,31 +0,0 @@
-clause Edge("g", "h")
-clause Edge("g", "d")
-clause Edge("e", "d")
-clause Edge("h", "f")
-clause Edge("e", "f")
-clause Edge("a", "e")
-clause Edge("a", "b")
-clause Edge("b", "f")
-clause Edge("b", "c")
-clause Edge("f", "c")
-
-clause Path(x, x)
------------- {}
-
-clause Path(x, y)
------------- {
-  Edge(x, z)
-  Path(z, y)
-}
-
-print find x {
-  Path("g", x)
-}
-
-print find x {
-  Path(x, "h")
-}
-
-print find [x, y] {
-  Path(x, y)
-}
diff --git a/docs/books/clause-and-effect/01-party-pairs.ch b/docs/examples/books/clause-and-effect/01-party-pairs.ch
similarity index 73%
rename from docs/books/clause-and-effect/01-party-pairs.ch
rename to docs/examples/books/clause-and-effect/01-party-pairs.ch
index 140d0ef9..3ecdae13 100644
--- a/docs/books/clause-and-effect/01-party-pairs.ch
+++ b/docs/examples/books/clause-and-effect/01-party-pairs.ch
@@ -1,10 +1,10 @@
-clause Male({ name: "bertram" })
-clause Male({ name: "percival" })
+relation Male({ name: "bertram" })
+relation Male({ name: "percival" })
 
-clause Female({ name: "lucinda" })
-clause Female({ name: "camilla" })
+relation Female({ name: "lucinda" })
+relation Female({ name: "camilla" })
 
-clause Pair({ male, female }) -- {
+relation Pair({ male, female }) -- {
   Male({ name: male })
   Female({ name: female })
 }
diff --git a/docs/books/clause-and-effect/01-party-pairs.ch.out b/docs/examples/books/clause-and-effect/01-party-pairs.ch.out
similarity index 100%
rename from docs/books/clause-and-effect/01-party-pairs.ch.out
rename to docs/examples/books/clause-and-effect/01-party-pairs.ch.out
diff --git a/docs/books/clause-and-effect/02-drinking-pairs.ch b/docs/examples/books/clause-and-effect/02-drinking-pairs.ch
similarity index 52%
rename from docs/books/clause-and-effect/02-drinking-pairs.ch
rename to docs/examples/books/clause-and-effect/02-drinking-pairs.ch
index c7e150b6..40325c2a 100644
--- a/docs/books/clause-and-effect/02-drinking-pairs.ch
+++ b/docs/examples/books/clause-and-effect/02-drinking-pairs.ch
@@ -1,11 +1,11 @@
-clause Drink({ person: "john", alcohol: "martini" })
-clause Drink({ person: "mary", alcohol: "gin" })
-clause Drink({ person: "susan", alcohol: "vodka" })
-clause Drink({ person: "john", alcohol: "gin" })
-clause Drink({ person: "fred", alcohol: "gin" })
-clause Drink({ person: "fred", alcohol: "vodka" })
+relation Drink({ person: "john", alcohol: "martini" })
+relation Drink({ person: "mary", alcohol: "gin" })
+relation Drink({ person: "susan", alcohol: "vodka" })
+relation Drink({ person: "john", alcohol: "gin" })
+relation Drink({ person: "fred", alcohol: "gin" })
+relation Drink({ person: "fred", alcohol: "vodka" })
 
-clause Friendship({ left, right, alcohol })
+relation Friendship({ left, right, alcohol })
 ------------------------------------ {
   Drink({ person: left, alcohol })
   Drink({ person: right, alcohol })
diff --git a/docs/books/clause-and-effect/02-drinking-pairs.ch.out b/docs/examples/books/clause-and-effect/02-drinking-pairs.ch.out
similarity index 100%
rename from docs/books/clause-and-effect/02-drinking-pairs.ch.out
rename to docs/examples/books/clause-and-effect/02-drinking-pairs.ch.out
diff --git a/docs/examples/books/clause-and-effect/03-affordable-journeys.ch b/docs/examples/books/clause-and-effect/03-affordable-journeys.ch
new file mode 100644
index 00000000..32bbcafd
--- /dev/null
+++ b/docs/examples/books/clause-and-effect/03-affordable-journeys.ch
@@ -0,0 +1,37 @@
+relation Border("sussex", "kent")
+relation Border("sussex", "surrey")
+relation Border("surrey", "kent")
+relation Border("hampshire", "sussex")
+relation Border("hampshire", "surrey")
+relation Border("hampshire", "berkshire")
+relation Border("berkshire", "surrey")
+relation Border("wiltshire", "hampshire")
+relation Border("wiltshire", "berkshire")
+
+relation Adjacent(x, y)
+---------------- border {
+  Border(x, y)
+}
+
+relation Adjacent(x, y)
+---------------- symmetry {
+  Border(y, x)
+}
+
+relation Affordable(x, y)
+-------------------- {
+  Adjacent(x, z)
+  Adjacent(z, y)
+}
+
+print find to_kent {
+  Affordable(to_kent, "kent")
+}
+
+print find to_sussex {
+  Affordable("sussex", to_sussex)
+}
+
+print find [x, y] {
+  Affordable(x, y)
+}
diff --git a/docs/books/clause-and-effect/03-affordable-journeys.ch.out b/docs/examples/books/clause-and-effect/03-affordable-journeys.ch.out
similarity index 100%
rename from docs/books/clause-and-effect/03-affordable-journeys.ch.out
rename to docs/examples/books/clause-and-effect/03-affordable-journeys.ch.out
diff --git a/docs/examples/books/clause-and-effect/04-acyclic-directed-graph.ch b/docs/examples/books/clause-and-effect/04-acyclic-directed-graph.ch
new file mode 100644
index 00000000..b8f30eba
--- /dev/null
+++ b/docs/examples/books/clause-and-effect/04-acyclic-directed-graph.ch
@@ -0,0 +1,31 @@
+relation Edge("g", "h")
+relation Edge("g", "d")
+relation Edge("e", "d")
+relation Edge("h", "f")
+relation Edge("e", "f")
+relation Edge("a", "e")
+relation Edge("a", "b")
+relation Edge("b", "f")
+relation Edge("b", "c")
+relation Edge("f", "c")
+
+relation Path(x, x)
+------------ {}
+
+relation Path(x, y)
+------------ {
+  Edge(x, z)
+  Path(z, y)
+}
+
+print find x {
+  Path("g", x)
+}
+
+print find x {
+  Path(x, "h")
+}
+
+print find [x, y] {
+  Path(x, y)
+}
diff --git a/docs/books/clause-and-effect/04-acyclic-directed-graph.ch.out b/docs/examples/books/clause-and-effect/04-acyclic-directed-graph.ch.out
similarity index 100%
rename from docs/books/clause-and-effect/04-acyclic-directed-graph.ch.out
rename to docs/examples/books/clause-and-effect/04-acyclic-directed-graph.ch.out
diff --git a/docs/books/clause-and-effect/05-member.ch b/docs/examples/books/clause-and-effect/05-member.ch
similarity index 80%
rename from docs/books/clause-and-effect/05-member.ch
rename to docs/examples/books/clause-and-effect/05-member.ch
index c8a24971..0442c9bc 100644
--- a/docs/books/clause-and-effect/05-member.ch
+++ b/docs/examples/books/clause-and-effect/05-member.ch
@@ -1,7 +1,7 @@
-clause Member(element, [element | _tail])
+relation Member(element, [element | _tail])
 ------------------------------------ here {}
 
-clause Member(element, [_head | tail])
+relation Member(element, [_head | tail])
 --------------------------------- there {
   Member(element, tail)
 }
diff --git a/docs/books/clause-and-effect/05-member.ch.out b/docs/examples/books/clause-and-effect/05-member.ch.out
similarity index 100%
rename from docs/books/clause-and-effect/05-member.ch.out
rename to docs/examples/books/clause-and-effect/05-member.ch.out
diff --git a/docs/books/clause-and-effect/06-length-of-a-list.ch b/docs/examples/books/clause-and-effect/06-length-of-a-list.ch
similarity index 86%
rename from docs/books/clause-and-effect/06-length-of-a-list.ch
rename to docs/examples/books/clause-and-effect/06-length-of-a-list.ch
index 8d648e02..5ea77f4e 100644
--- a/docs/books/clause-and-effect/06-length-of-a-list.ch
+++ b/docs/examples/books/clause-and-effect/06-length-of-a-list.ch
@@ -1,11 +1,11 @@
 import { Zero, Add1, One, Two } from "../../std/nat/index.ch"
 
-clause Length([], n)
+relation Length([], n)
 -------------------- {
   Zero(n)
 }
 
-clause Length([_head | tail], n)
+relation Length([_head | tail], n)
 -------------------------------- {
   Add1(prev, n)
   Length(tail, prev)
diff --git a/docs/books/clause-and-effect/08-maximum-of-a-list.ch b/docs/examples/books/clause-and-effect/08-maximum-of-a-list.ch
similarity index 79%
rename from docs/books/clause-and-effect/08-maximum-of-a-list.ch
rename to docs/examples/books/clause-and-effect/08-maximum-of-a-list.ch
index 9f019280..0e3accdc 100644
--- a/docs/books/clause-and-effect/08-maximum-of-a-list.ch
+++ b/docs/examples/books/clause-and-effect/08-maximum-of-a-list.ch
@@ -1,13 +1,13 @@
-// clause Max(null, n, n)
+// relation Max(null, n, n)
 // ---------------- {}
 
-// clause Max(cons(x, rest), n, max)
+// relation Max(cons(x, rest), n, max)
 // ---------------------------- {
 //   Max(rest, x, max)
 //   x > n
 // }
 
-// clause Max(cons (x, rest), n, max)
+// relation Max(cons (x, rest), n, max)
 // ---------------------------- {
 //   Max(rest, n, max)
 //   x <= n
diff --git a/docs/books/clause-and-effect/09-searching-a-cyclic-graph.ch b/docs/examples/books/clause-and-effect/09-searching-a-cyclic-graph.ch
similarity index 61%
rename from docs/books/clause-and-effect/09-searching-a-cyclic-graph.ch
rename to docs/examples/books/clause-and-effect/09-searching-a-cyclic-graph.ch
index 15e389b6..b680311c 100644
--- a/docs/books/clause-and-effect/09-searching-a-cyclic-graph.ch
+++ b/docs/examples/books/clause-and-effect/09-searching-a-cyclic-graph.ch
@@ -1,30 +1,30 @@
-clause Edge("g", "h")
-clause Edge("d", "a")
-clause Edge("g", "d")
-clause Edge("e", "d")
-clause Edge("h", "f")
-clause Edge("e", "f")
-clause Edge("a", "e")
-clause Edge("a", "b")
-clause Edge("b", "f")
-clause Edge("b", "c")
-clause Edge("f", "c")
+relation Edge("g", "h")
+relation Edge("d", "a")
+relation Edge("g", "d")
+relation Edge("e", "d")
+relation Edge("h", "f")
+relation Edge("e", "f")
+relation Edge("a", "e")
+relation Edge("a", "b")
+relation Edge("b", "f")
+relation Edge("b", "c")
+relation Edge("f", "c")
 
 // "a", "e", "d" -- in a loop
 
 // We define `Legal` to rule out loop -- to avoid searching in a loop
 
-clause Legal(_, [])
+relation Legal(_, [])
 
-clause Legal(z, [head | tail])
+relation Legal(z, [head | tail])
 ---------------------------- {
   NotEqual(z, head)
   Legal(z, tail)
 }
 
-clause Path(x, x, _occurs)
+relation Path(x, x, _occurs)
 
-clause Path(x, y, occurs)
+relation Path(x, y, occurs)
 ------------------------ {
   Edge(x, z)
   Legal(z, occurs)
diff --git a/docs/books/clause-and-effect/09-searching-a-cyclic-graph.ch.out b/docs/examples/books/clause-and-effect/09-searching-a-cyclic-graph.ch.out
similarity index 100%
rename from docs/books/clause-and-effect/09-searching-a-cyclic-graph.ch.out
rename to docs/examples/books/clause-and-effect/09-searching-a-cyclic-graph.ch.out
diff --git a/docs/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch b/docs/examples/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch
similarity index 87%
rename from docs/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch
rename to docs/examples/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch
index 29639b4a..e28b7bba 100644
--- a/docs/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch
+++ b/docs/examples/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch
@@ -10,18 +10,18 @@
 // Here is the information about Ben Bitdiddle,
 // the resident computer wizard:
 
-clause Job({
+relation Job({
   name: "Bitdiddle Ben",
   dept: "computer",
   role: "wizard",
 })
 
-clause Salary({
+relation Salary({
   name: "Bitdiddle Ben",
   amount: 60000,
 })
 
-clause Address({
+relation Address({
   name: "Bitdiddle Ben",
   town: "Slumerville",
   road: "Ridge Road",
@@ -34,71 +34,71 @@ clause Address({
 
 // Here is the information about them:
 
-clause Address({
+relation Address({
   name: "Hacker Alyssa P",
   town: "Cambridge",
   road: "Mass Ave",
   door: 78,
 })
 
-clause Job({
+relation Job({
   name: "Hacker Alyssa P",
   dept: "computer",
   role: "programmer",
 })
 
-clause Salary({
+relation Salary({
   name: "Hacker Alyssa P",
   amount: 40000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Hacker Alyssa P",
   master: "Bitdiddle Ben",
 })
 
-clause Address({
+relation Address({
   name: "Fect Cy D",
   town: "Cambridge",
   road: "Ames Street",
   door: 3,
 })
 
-clause Job({
+relation Job({
   name: "Fect Cy D",
   dept: "computer",
   role: "programmer",
 })
 
-clause Salary({
+relation Salary({
   name: "Fect Cy D",
   amount: 35000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Fect Cy D",
   master: "Bitdiddle Ben",
 })
 
-clause Address({
+relation Address({
   name: "Tweakit Lem E",
   town: "Boston",
   road: "Bay State Road",
   door: 22,
 })
 
-clause Job({
+relation Job({
   name: "Tweakit Lem E",
   dept: "computer",
   role: "technician",
 })
 
-clause Salary({
+relation Salary({
   name: "Tweakit Lem E",
   amount: 25000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Tweakit Lem E",
   master: "Bitdiddle Ben",
 })
@@ -106,25 +106,25 @@ clause Supervisor({
 // There is also a programmer trainee,
 // who is supervised by Alyssa:
 
-clause Address({
+relation Address({
   name: "Reasoner Louis",
   town: "Slumerville",
   road: "Pine Tree Road",
   door: 80,
 })
 
-clause Job({
+relation Job({
   name: "Reasoner Louis",
   dept: "computer",
   role: "programmer trainee",
 })
 
-clause Salary({
+relation Salary({
   name: "Reasoner Louis",
   amount: 30000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Reasoner Louis",
   master: "Hacker Alyssa P",
 })
@@ -132,25 +132,25 @@ clause Supervisor({
 // Ben is a high-level employee.
 // His supervisor is the company's big wheel himself:
 
-clause Supervisor({
+relation Supervisor({
   slave: "Bitdiddle Ben",
   master: "Warbucks Oliver",
 })
 
-clause Address({
+relation Address({
   name: "Warbucks Oliver",
   town: "Swellesley",
   road: "The Manor",
   door: 1,
 })
 
-clause Job({
+relation Job({
   name: "Warbucks Oliver",
   dept: "administration",
   role: "big wheel",
 })
 
-clause Salary({
+relation Salary({
   name: "Warbucks Oliver",
   amount: 150000,
 })
@@ -159,73 +159,73 @@ clause Salary({
 // the company has an accounting division,
 // consisting of a chief accountant and his assistant:
 
-clause Address({
+relation Address({
   name: "Scrooge Eben",
   town: "Weston",
   road: "Shady Lane",
   door: 10,
 })
 
-clause Job({
+relation Job({
   name: "Scrooge Eben",
   dept: "accounting",
   role: "chief accountant",
 })
 
-clause Salary({
+relation Salary({
   name: "Scrooge Eben",
   amount: 75000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Scrooge Eben",
   master: "Warbucks Oliver",
 })
 
-clause Address({
+relation Address({
   name: "Cratchet Robert",
   town: "Allston",
   road: "N Harvard Street",
   door: 16,
 })
 
-clause Job({
+relation Job({
   name: "Cratchet Robert",
   dept: "accounting",
   role: "scrivener",
 })
 
-clause Salary({
+relation Salary({
   name: "Cratchet Robert",
   amount: 18000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Cratchet Robert",
   master: "Scrooge Eben",
 })
 
 // There is also a secretary for the big wheel:
 
-clause Address({
+relation Address({
   name: "Aull DeWitt",
   town: "Slumerville",
   road: "Onion Square",
   door: 5,
 })
 
-clause Job({
+relation Job({
   name: "Aull DeWitt",
   dept: "administration",
   role: "secretary",
 })
 
-clause Salary({
+relation Salary({
   name: "Aull DeWitt",
   amount: 25000,
 })
 
-clause Supervisor({
+relation Supervisor({
   slave: "Aull DeWitt",
   master: "Warbucks Oliver",
 })
@@ -238,7 +238,7 @@ clause Supervisor({
 // the jobs of both a computer programmer
 // and a computer technician:
 
-clause Competence({
+relation Competence({
   can: {
     dept: "computer",
     role: "wizard",
@@ -249,7 +249,7 @@ clause Competence({
   },
 })
 
-clause Competence({
+relation Competence({
   can: {
     dept: "computer",
     role: "wizard",
@@ -262,7 +262,7 @@ clause Competence({
 
 // A computer programmer could fill in for a trainee:
 
-clause Competence({
+relation Competence({
   can: {
     dept: "computer",
     role: "programmer",
@@ -275,7 +275,7 @@ clause Competence({
 
 // Also, as is well known,
 
-clause Competence({
+relation Competence({
   can: {
     dept: "administration",
     role: "secretary",
@@ -350,7 +350,7 @@ print find x {
 
 // We can use the following syntax to create rules.
 
-clause ComputerDeptSlave({ slave })
+relation ComputerDeptSlave({ slave })
 ---------------------------- {
   Job({ name: slave, dept: "computer" })
   Supervisor({ slave })
@@ -362,7 +362,7 @@ print find slave {
 
 // TODO We do not have `not` yet.
 
-// clause Bigshot({ name, dept })
+// relation Bigshot({ name, dept })
 // ------------------------ {
 //   Job({ name, dept })
 //   not {
@@ -380,7 +380,7 @@ print find slave {
 
 // TODO `>=`
 
-// clause NotSoPoor({ name, amount })
+// relation NotSoPoor({ name, amount })
 // ---------------------------- {
 //   Salary({ name, amount })
 //   FD::GtEq(amount, 40000)
diff --git a/docs/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch.out b/docs/examples/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch.out
similarity index 100%
rename from docs/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch.out
rename to docs/examples/books/structure-and-interpretation-of-computer-programs/a-boston-high-tech-company.ch.out
diff --git a/docs/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md b/docs/examples/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md
similarity index 92%
rename from docs/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md
rename to docs/examples/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md
index a2a40f9c..1d7fa3bc 100644
--- a/docs/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md
+++ b/docs/examples/books/structure-and-interpretation-of-computer-programs/logic-as-programs.md
@@ -31,10 +31,10 @@ cons(1, cons(2, cons(3, cons(4, null))))
 **Relation:**
 
 ```ch
-clause Append([], right, right)
+relation Append([], right, right)
 ---------------------------- {}
 
-clause Append(
+relation Append(
   [head | left_tail],
   right,
   [head | result_tail],
@@ -87,13 +87,13 @@ cons(1, cons(2, cons(3, cons(4, null))))
 **Relation:**
 
 ```ch todo
-clause Merge(null, right, right)
+relation Merge(null, right, right)
 ------------------------ {}
 
-clause Merge(left, null, left)
+relation Merge(left, null, left)
 ------------------------ {}
 
-clause Merge(
+relation Merge(
   [left_head | left_tail],
   [head | right_tail],
   [head | result_tail],
@@ -103,7 +103,7 @@ clause Merge(
   FD::Gt(left_head, head)
 }
 
-clause Merge(
+relation Merge(
   [head | left_tail],
   [right_head | right_tail],
   [head | result_tail],
diff --git a/docs/books/the-reasoned-schemer/01-playthings.ch b/docs/examples/books/the-reasoned-schemer/01-playthings.ch
similarity index 93%
rename from docs/books/the-reasoned-schemer/01-playthings.ch
rename to docs/examples/books/the-reasoned-schemer/01-playthings.ch
index 8e209be3..52a96cf5 100644
--- a/docs/books/the-reasoned-schemer/01-playthings.ch
+++ b/docs/examples/books/the-reasoned-schemer/01-playthings.ch
@@ -1,6 +1,6 @@
-export clause Succeed()
+export relation Succeed()
 
-export clause Fail()
+export relation Fail()
 -------- {
   Equal(1, 2)
 }
@@ -107,12 +107,12 @@ print find q {
   Equal("corn", q)
 }
 
-clause Teacup(t)
+relation Teacup(t)
 --------------- tea {
   Equal(t, "tea")
 }
 
-clause Teacup(t)
+relation Teacup(t)
 --------------- cup {
   Equal(t, "cup")
 }
diff --git a/docs/books/the-reasoned-schemer/01-playthings.ch.out b/docs/examples/books/the-reasoned-schemer/01-playthings.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/01-playthings.ch.out
rename to docs/examples/books/the-reasoned-schemer/01-playthings.ch.out
diff --git a/docs/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch b/docs/examples/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch
similarity index 91%
rename from docs/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch
rename to docs/examples/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch
index af639a56..4260f54b 100644
--- a/docs/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch
+++ b/docs/examples/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch
@@ -1,4 +1,4 @@
-export clause Car(p, a)
+export relation Car(p, a)
 ---------- {
   Equal([a | _d], p)
 }
@@ -22,7 +22,7 @@ print find r {
   Equal([x | y], r)
 }
 
-export clause Cdr(p, d)
+export relation Cdr(p, d)
 ---------- {
   Equal([_a | d], p)
 }
@@ -53,12 +53,12 @@ print find l {
   Equal(x, "a")
 }
 
-// clause Cons(a, d, p)
+// relation Cons(a, d, p)
 // --------------- {
 //   Equal([a | d], p)
 // }
 
-export clause Cons(a, d, p)
+export relation Cons(a, d, p)
 --------------- {
   Car(p, a)
   Cdr(p, d)
@@ -101,7 +101,7 @@ print find l {
   Equal("o", y)
 }
 
-export clause Null(x)
+export relation Null(x)
 ---------- {
   Equal([], x)
 }
@@ -122,7 +122,7 @@ print find r {
   Equal([_x, _y, "salad"], r)
 }
 
-clause Pair(p)
+relation Pair(p)
 ------ {
   Cons(_a, _d, p)
 }
@@ -147,14 +147,14 @@ print find r {
   Pair([r])
 }
 
-// clause Singleton(l)
+// relation Singleton(l)
 // ----------- {
 //   Pair(l)
 //   Cdr(l, d)
 //   Null(d)
 // }
 
-clause Singleton(l)
+relation Singleton(l)
 ----------- {
   Cdr(l, d)
   Null(d)
diff --git a/docs/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch.out b/docs/examples/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch.out
rename to docs/examples/books/the-reasoned-schemer/02-teaching-old-toys-new-tricks.ch.out
diff --git a/docs/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch b/docs/examples/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch
similarity index 87%
rename from docs/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch
rename to docs/examples/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch
index af155e60..c904e181 100644
--- a/docs/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch
+++ b/docs/examples/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch
@@ -1,12 +1,12 @@
 import { Succeed, Fail } from "01-playthings.ch"
 import { Null, Cons, Car, Cdr } from "02-teaching-old-toys-new-tricks.ch"
 
-clause List(l)
+relation List(l)
 ----------- {
   Null(l)
 }
 
-clause List(l)
+relation List(l)
 ------------- {
   Cdr(l, d)
   List(d)
@@ -24,12 +24,12 @@ print find x limit 5 {
   List(["a", "b" | x])
 }
 
-clause ListOfLists(l)
+relation ListOfLists(l)
 ------------- {
   Null(l)
 }
 
-clause ListOfLists(l)
+relation ListOfLists(l)
 ------------- {
   Car(l, a)
   List(a)
@@ -57,17 +57,17 @@ print find x limit 5 {
   ListOfLists([["a", "b"], ["c", "d"] | x])
 }
 
-clause Singleton(l)
+relation Singleton(l)
 ----------- {
   Equal(l, [_])
 }
 
-clause ListOfSingletons(l)
+relation ListOfSingletons(l)
 ------------------- {
   Null(l)
 }
 
-clause ListOfSingletons(l)
+relation ListOfSingletons(l)
 -------------------- {
   Car(l, a)
   Singleton(a)
@@ -95,24 +95,24 @@ print find out limit 5 {
 
 // NOTE By "The Law of Fail", we can drop the following clause.
 
-// clause Member(x, l)
+// relation Member(x, l)
 // ------------- {
 //   Null(l)
 //   Fail()
 // }
 
-// clause Member(x, l)
+// relation Member(x, l)
 // ------------- {
 //   Car(l, a)
 //   Equal(x, a)
 // }
 
-clause Member(x, l)
+relation Member(x, l)
 ------------- {
   Car(l, x)
 }
 
-clause Member(x, l)
+relation Member(x, l)
 ------------- {
   Cdr(l, d)
   Member(x, d)
@@ -159,14 +159,14 @@ print find l limit 5 {
   Member("tofu", l)
 }
 
-clause ProperMember(x, l)
+relation ProperMember(x, l)
 ------------------- {
   Car(l, x)
   Cdr(l, d)
   List(d)
 }
 
-clause ProperMember(x, l)
+relation ProperMember(x, l)
 ------------------- {
   Cdr(l, d)
   ProperMember(x, d)
diff --git a/docs/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch.out b/docs/examples/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch.out
rename to docs/examples/books/the-reasoned-schemer/03-seeing-old-friends-in-new-ways.ch.out
diff --git a/docs/books/the-reasoned-schemer/04-double-your-fun.ch b/docs/examples/books/the-reasoned-schemer/04-double-your-fun.ch
similarity index 93%
rename from docs/books/the-reasoned-schemer/04-double-your-fun.ch
rename to docs/examples/books/the-reasoned-schemer/04-double-your-fun.ch
index b35571c5..00c31631 100644
--- a/docs/books/the-reasoned-schemer/04-double-your-fun.ch
+++ b/docs/examples/books/the-reasoned-schemer/04-double-your-fun.ch
@@ -1,12 +1,12 @@
 import { Null, Cons, Car, Cdr } from "02-teaching-old-toys-new-tricks.ch"
 
-clause Append(l, t, out)
+relation Append(l, t, out)
 ------------------ {
   Null(l)
   Equal(out, t)
 }
 
-clause Append(l, t, out)
+relation Append(l, t, out)
 ------------------ {
   Cdr(l, d)
   Append(d, t, res)
@@ -110,13 +110,13 @@ print find [x, y] limit 6 {
   )
 }
 
-clause Unwrap(x, out)
+relation Unwrap(x, out)
 --------------- {
   Car(x, a)
   Unwrap(a, out)
 }
 
-clause Unwrap(x, out)
+relation Unwrap(x, out)
 --------------- {
   Equal(x, out)
 }
diff --git a/docs/books/the-reasoned-schemer/04-double-your-fun.ch.out b/docs/examples/books/the-reasoned-schemer/04-double-your-fun.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/04-double-your-fun.ch.out
rename to docs/examples/books/the-reasoned-schemer/04-double-your-fun.ch.out
diff --git a/docs/books/the-reasoned-schemer/05-members-only.ch b/docs/examples/books/the-reasoned-schemer/05-members-only.ch
similarity index 93%
rename from docs/books/the-reasoned-schemer/05-members-only.ch
rename to docs/examples/books/the-reasoned-schemer/05-members-only.ch
index e4e3a3ad..69cd03b2 100644
--- a/docs/books/the-reasoned-schemer/05-members-only.ch
+++ b/docs/examples/books/the-reasoned-schemer/05-members-only.ch
@@ -1,12 +1,12 @@
 import { Null, Cons, Car, Cdr } from "02-teaching-old-toys-new-tricks.ch"
 
-clause Mem(x, l, out)
+relation Mem(x, l, out)
 --------------- {
   Car(l, x)
   Equal(out, l)
 }
 
-clause Mem(x, l, out)
+relation Mem(x, l, out)
 --------------- {
   Cdr(l, d)
   Mem(x, d, out)
@@ -68,19 +68,19 @@ print find [x, y] limit 5 {
   Mem("fig", ["fig", "d", "fig", "e" | y], x)
 }
 
-clause Rember(_x, l, out)
+relation Rember(_x, l, out)
 ------------------ {
   Null(l)
   Null(out)
 }
 
-clause Rember(x, l, out)
+relation Rember(x, l, out)
 ------------------ {
   Car(l, x)
   Cdr(l, out)
 }
 
-clause Rember(x, l, out)
+relation Rember(x, l, out)
 ------------------ {
   Cdr(l, d)
   Rember(x, d, res)
diff --git a/docs/books/the-reasoned-schemer/05-members-only.ch.out b/docs/examples/books/the-reasoned-schemer/05-members-only.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/05-members-only.ch.out
rename to docs/examples/books/the-reasoned-schemer/05-members-only.ch.out
diff --git a/docs/books/the-reasoned-schemer/06-the-fun-never-ends.ch b/docs/examples/books/the-reasoned-schemer/06-the-fun-never-ends.ch
similarity index 93%
rename from docs/books/the-reasoned-schemer/06-the-fun-never-ends.ch
rename to docs/examples/books/the-reasoned-schemer/06-the-fun-never-ends.ch
index 38de1d73..6820cce6 100644
--- a/docs/books/the-reasoned-schemer/06-the-fun-never-ends.ch
+++ b/docs/examples/books/the-reasoned-schemer/06-the-fun-never-ends.ch
@@ -1,11 +1,11 @@
 import { Succeed, Fail } from "01-playthings.ch"
 
-clause Always()
+relation Always()
 --------- {
   Succeed()
 }
 
-clause Always()
+relation Always()
 --------- {
   Always()
 }
@@ -45,7 +45,7 @@ print find q {
   Always()
 }
 
-clause Never()
+relation Never()
 --------- {
   Never()
 }
diff --git a/docs/books/the-reasoned-schemer/06-the-fun-never-ends.ch.out b/docs/examples/books/the-reasoned-schemer/06-the-fun-never-ends.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/06-the-fun-never-ends.ch.out
rename to docs/examples/books/the-reasoned-schemer/06-the-fun-never-ends.ch.out
diff --git a/docs/books/the-reasoned-schemer/07-a-bit-too-much.ch b/docs/examples/books/the-reasoned-schemer/07-a-bit-too-much.ch
similarity index 73%
rename from docs/books/the-reasoned-schemer/07-a-bit-too-much.ch
rename to docs/examples/books/the-reasoned-schemer/07-a-bit-too-much.ch
index 399c1397..24721f02 100644
--- a/docs/books/the-reasoned-schemer/07-a-bit-too-much.ch
+++ b/docs/examples/books/the-reasoned-schemer/07-a-bit-too-much.ch
@@ -1,14 +1,14 @@
-clause Bit(0)
-clause Bit(1)
+relation Bit(0)
+relation Bit(1)
 
 print find x {
   Bit(x)
 }
 
-clause BitXor(0, 0, 0)
-clause BitXor(0, 1, 1)
-clause BitXor(1, 0, 1)
-clause BitXor(1, 1, 0)
+relation BitXor(0, 0, 0)
+relation BitXor(0, 1, 1)
+relation BitXor(1, 0, 1)
+relation BitXor(1, 1, 0)
 
 print find [x, y] {
   BitXor(x, y, 0)
@@ -22,10 +22,10 @@ print find [x, y, r] {
   BitXor(x, y, r)
 }
 
-clause BitAnd(0, 0, 0)
-clause BitAnd(0, 1, 0)
-clause BitAnd(1, 0, 0)
-clause BitAnd(1, 1, 1)
+relation BitAnd(0, 0, 0)
+relation BitAnd(0, 1, 0)
+relation BitAnd(1, 0, 0)
+relation BitAnd(1, 1, 1)
 
 print find [x, y] {
   BitAnd(x, y, 1)
@@ -33,7 +33,7 @@ print find [x, y] {
 
 // x + y = r + 2 * c
 
-clause HalfAdder(x, y, r, c)
+relation HalfAdder(x, y, r, c)
 ---------------------- {
   BitXor(x, y, r)
   BitAnd(x, y, c)
@@ -49,7 +49,7 @@ print find [x, y, r, c] {
 
 // b + x + y = r + 2 * c
 
-clause FullAdder(b, x, y, r, c)
+relation FullAdder(b, x, y, r, c)
 ------------------------- {
   HalfAdder(x, y, w, xy)
   HalfAdder(w, b, r, wz)
@@ -68,7 +68,7 @@ print find [b, x, y, r, c] {
   FullAdder(b, x, y, r, c)
 }
 
-export clause Positive(n)
+export relation Positive(n)
 ---------------- {
   Equal([_a | _d], n)
 }
@@ -89,7 +89,7 @@ print find r {
   Positive(r)
 }
 
-export clause GreaterThanOne(n)
+export relation GreaterThanOne(n)
 --------------------- {
   Equal([_a, _ad | _dd], n)
 }
@@ -114,14 +114,14 @@ print find r {
   GreaterThanOne(r)
 }
 
-clause Adder(0, n, [], n)
-clause Adder(0, [], m, m) -- { Positive(m) }
-clause Adder(1, n, [], r) -- { Adder(0, n, [1], r) }
-clause Adder(1, [], m, r) -- { Positive(m) Adder(0, [1], m, r) }
-clause Adder(b, [1], [1], [a, c]) -- { FullAdder(b, 1, 1, a, c) }
-clause Adder(b, [1], m, r) -- { GenAdder(b, [1], m, r) }
-clause Adder(b, n, [1], r) -- { GreaterThanOne(n) GreaterThanOne(r) Adder(b, [1], n, r) }
-clause Adder(b, n, m, r) -- { GreaterThanOne(n) GenAdder(b, n, m, r) }
+relation Adder(0, n, [], n)
+relation Adder(0, [], m, m) -- { Positive(m) }
+relation Adder(1, n, [], r) -- { Adder(0, n, [1], r) }
+relation Adder(1, [], m, r) -- { Positive(m) Adder(0, [1], m, r) }
+relation Adder(b, [1], [1], [a, c]) -- { FullAdder(b, 1, 1, a, c) }
+relation Adder(b, [1], m, r) -- { GenAdder(b, [1], m, r) }
+relation Adder(b, n, [1], r) -- { GreaterThanOne(n) GreaterThanOne(r) Adder(b, [1], n, r) }
+relation Adder(b, n, m, r) -- { GreaterThanOne(n) GenAdder(b, n, m, r) }
 
 // Given the carry bit b,
 // and the numbers n, m, and r,
@@ -129,7 +129,7 @@ clause Adder(b, n, m, r) -- { GreaterThanOne(n) GenAdder(b, n, m, r) }
 // provided that n is positive
 // and m and r are greater than one.
 
-clause GenAdder(b, n, m, r)
+relation GenAdder(b, n, m, r)
 ------------------------- {
   Equal([a | x], n)
   Equal([d | y], m)  Positive(y)
@@ -162,7 +162,7 @@ print find [x, y] {
   Adder(0, x, y, [1, 0, 1])
 }
 
-export clause Add(x, y, r)
+export relation Add(x, y, r)
 --------------------- {
   Adder(0, x, y, r)
 }
@@ -183,7 +183,7 @@ print find [x, y] {
   Add(x, y, [1, 0, 1])
 }
 
-clause Sub(n, m, k)
+relation Sub(n, m, k)
 ---------------- {
   Add(m, k, n)
 }
@@ -216,8 +216,8 @@ print find q {
 //   Add(x, y, [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1])
 // }
 
-clause Length([], [])
-clause Length([_a | d], n) -- {
+relation Length([], [])
+relation Length([_a | d], n) -- {
   Add([1], res, n)
   Length(d, res)
 }
diff --git a/docs/books/the-reasoned-schemer/07-a-bit-too-much.ch.out b/docs/examples/books/the-reasoned-schemer/07-a-bit-too-much.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/07-a-bit-too-much.ch.out
rename to docs/examples/books/the-reasoned-schemer/07-a-bit-too-much.ch.out
diff --git a/docs/books/the-reasoned-schemer/08-just-a-bit-more.ch b/docs/examples/books/the-reasoned-schemer/08-just-a-bit-more.ch
similarity index 63%
rename from docs/books/the-reasoned-schemer/08-just-a-bit-more.ch
rename to docs/examples/books/the-reasoned-schemer/08-just-a-bit-more.ch
index d97d8cd9..de41268d 100644
--- a/docs/books/the-reasoned-schemer/08-just-a-bit-more.ch
+++ b/docs/examples/books/the-reasoned-schemer/08-just-a-bit-more.ch
@@ -4,17 +4,17 @@ import {
   Add,
 } from "07-a-bit-too-much.ch"
 
-clause Mul([], _m, [])
-clause Mul(n, [], []) -- { Positive(n) }
-clause Mul([1], m, m) -- { Positive(m) }
-clause Mul(n, [1], n) -- { GreaterThanOne(n) }
-clause Mul([0 | x], m, [0 | z]) -- { Positive(x) Positive(z) GreaterThanOne(m) Mul(x, m, z) }
-clause Mul([1 | x], [0 | y], p) -- { Positive(x) Positive(y) Mul([0 | y], [1 | x], p) }
-clause Mul([1 | x], [1 | y], p) -- { Positive(x) Positive(y) MulOdd(x, [1 | x], [1 | y], p) }
+relation Mul([], _m, [])
+relation Mul(n, [], []) -- { Positive(n) }
+relation Mul([1], m, m) -- { Positive(m) }
+relation Mul(n, [1], n) -- { GreaterThanOne(n) }
+relation Mul([0 | x], m, [0 | z]) -- { Positive(x) Positive(z) GreaterThanOne(m) Mul(x, m, z) }
+relation Mul([1 | x], [0 | y], p) -- { Positive(x) Positive(y) Mul([0 | y], [1 | x], p) }
+relation Mul([1 | x], [1 | y], p) -- { Positive(x) Positive(y) MulOdd(x, [1 | x], [1 | y], p) }
 
 // x = (n - 1) / 2
 
-clause MulOdd(x, n, m, p)
+relation MulOdd(x, n, m, p)
 -------------------- {
   MulBound(q, p, n, m)
   Mul(x, m, q)
@@ -23,9 +23,9 @@ clause MulOdd(x, n, m, p)
 
 // NOTE Limit the length of the q above.
 
-clause MulBound([], p, _n, _m) -- { Positive(p) }
-clause MulBound([_a0 | x], [_a1 | y], [], [_a2 | z]) -- { MulBound(x, y, z, []) }
-clause MulBound([_a0 | x], [_a1 | y], [_a2 | z], m) -- { MulBound(x, y, z, m) }
+relation MulBound([], p, _n, _m) -- { Positive(p) }
+relation MulBound([_a0 | x], [_a1 | y], [], [_a2 | z]) -- { MulBound(x, y, z, []) }
+relation MulBound([_a0 | x], [_a1 | y], [_a2 | z], m) -- { MulBound(x, y, z, m) }
 
 print find [x, y, r] limit 10 {
   Mul(x, y, r)
@@ -74,9 +74,9 @@ print find p {
   Mul([1, 1, 1], [1, 1, 1, 1, 1, 1], p)
 }
 
-clause EqualLength([], [])
-clause EqualLength([1], [1])
-clause EqualLength([_a | x], [_b | y])
+relation EqualLength([], [])
+relation EqualLength([1], [1])
+relation EqualLength([_a | x], [_b | y])
 ----------------------------------- {
   Positive(x)
   Positive(y)
diff --git a/docs/books/the-reasoned-schemer/08-just-a-bit-more.ch.out b/docs/examples/books/the-reasoned-schemer/08-just-a-bit-more.ch.out
similarity index 100%
rename from docs/books/the-reasoned-schemer/08-just-a-bit-more.ch.out
rename to docs/examples/books/the-reasoned-schemer/08-just-a-bit-more.ch.out
diff --git a/docs/books/the-reasoned-schemer/09-thin-ice.ch b/docs/examples/books/the-reasoned-schemer/09-thin-ice.ch
similarity index 100%
rename from docs/books/the-reasoned-schemer/09-thin-ice.ch
rename to docs/examples/books/the-reasoned-schemer/09-thin-ice.ch
diff --git a/docs/books/the-reasoned-schemer/10-under-the-hood.ch b/docs/examples/books/the-reasoned-schemer/10-under-the-hood.ch
similarity index 100%
rename from docs/books/the-reasoned-schemer/10-under-the-hood.ch
rename to docs/examples/books/the-reasoned-schemer/10-under-the-hood.ch
diff --git a/docs/langs/lambda-closure.ch b/docs/examples/langs/lambda-closure.ch
similarity index 57%
rename from docs/langs/lambda-closure.ch
rename to docs/examples/langs/lambda-closure.ch
index 55bebb12..dc222b6c 100644
--- a/docs/langs/lambda-closure.ch
+++ b/docs/examples/langs/lambda-closure.ch
@@ -1,42 +1,42 @@
-clause Exp(Exp::Var(name)) -- { String(name) }
-clause Exp(Exp::Fn(name, ret)) -- { String(name) Exp(ret) }
-clause Exp(Exp::Ap(target, arg)) -- { Exp(target) Exp(arg) }
+relation Exp(Exp::Var(name)) -- { String(name) }
+relation Exp(Exp::Fn(name, ret)) -- { String(name) Exp(ret) }
+relation Exp(Exp::Ap(target, arg)) -- { Exp(target) Exp(arg) }
 
 print find exp limit 10 {
   Exp(exp)
 }
 
-clause Value(Value::Closure(name, ret, env)) -- {
+relation Value(Value::Closure(name, ret, env)) -- {
   String(name)
   Exp(ret)
   Env(env)
 }
 
-clause Env([])
-clause Env([[name, value] | rest]) -- {
+relation Env([])
+relation Env([[name, value] | rest]) -- {
   String(name)
   Value(value)
   Env(rest)
 }
 
-clause Lookup([[key, value] | _rest], key, value) -- here
-clause Lookup([[key, _value] | rest], name, found)
+relation Lookup([[key, value] | _rest], key, value) -- here
+relation Lookup([[key, _value] | rest], name, found)
 --------------------------------------------- there {
   NotEqual(key, name)
   Lookup(rest, name, found)
 }
 
-clause Eval(env, Exp::Var(name), value)
+relation Eval(env, Exp::Var(name), value)
 ---------------------------- var {
   Lookup(env, name, value)
 }
 
-clause Eval(env, Exp::Fn(name, ret), value)
+relation Eval(env, Exp::Fn(name, ret), value)
 ---------------------------------- fn {
   Equal(value, Value::Closure(name, ret, env))
 }
 
-clause Eval(env, Exp::Ap(target, arg), value)
+relation Eval(env, Exp::Ap(target, arg), value)
 ---------------------------------------- ap {
   Eval(env, target, Value::Closure(name, ret, env2))
   Eval(env, arg, argValue)
diff --git a/docs/langs/lambda-closure.ch.out b/docs/examples/langs/lambda-closure.ch.out
similarity index 100%
rename from docs/langs/lambda-closure.ch.out
rename to docs/examples/langs/lambda-closure.ch.out
diff --git a/docs/langs/lambda-simple-type.ch b/docs/examples/langs/lambda-simple-type.ch
similarity index 58%
rename from docs/langs/lambda-simple-type.ch
rename to docs/examples/langs/lambda-simple-type.ch
index 2d8c11a4..51d64e2b 100644
--- a/docs/langs/lambda-simple-type.ch
+++ b/docs/examples/langs/lambda-simple-type.ch
@@ -1,31 +1,31 @@
-clause Exp(Exp::Var(name)) -- { String(name) }
-clause Exp(Exp::Fn(name, ret)) -- { String(name) Exp(ret) }
-clause Exp(Exp::Ap(target, arg)) -- { Exp(target) Exp(arg) }
+relation Exp(Exp::Var(name)) -- { String(name) }
+relation Exp(Exp::Fn(name, ret)) -- { String(name) Exp(ret) }
+relation Exp(Exp::Ap(target, arg)) -- { Exp(target) Exp(arg) }
 
-clause Type(Type::Atom(name)) -- { String(name) }
-clause Type(Type::Arrow(argType, retType)) -- { Type(argType) Type(retType) }
+relation Type(Type::Atom(name)) -- { String(name) }
+relation Type(Type::Arrow(argType, retType)) -- { Type(argType) Type(retType) }
 
-clause Ctx([])
-clause Ctx([[name, type] | rest]) -- { String(name) Type(type) Ctx(rest) }
+relation Ctx([])
+relation Ctx([[name, type] | rest]) -- { String(name) Type(type) Ctx(rest) }
 
-clause Lookup([[key, value] | _rest], key, value)
-clause Lookup([[key, _value] | rest], name, found)
+relation Lookup([[key, value] | _rest], key, value)
+relation Lookup([[key, _value] | rest], name, found)
 -------------------------------------------- {
   NotEqual(key, name)
   Lookup(rest, name, found)
 }
 
-clause Check(ctx, Exp::Var(name), type)
+relation Check(ctx, Exp::Var(name), type)
 ---------------------------- {
   Lookup(ctx, name, type)
 }
 
-clause Check(ctx, Exp::Fn(name, ret), Type::Arrow(argType, retType))
+relation Check(ctx, Exp::Fn(name, ret), Type::Arrow(argType, retType))
 --------------------------------------------------- {
   Check([[name, argType] | ctx], ret, retType)
 }
 
-clause Check(ctx, Exp::Ap(target, arg), retType)
+relation Check(ctx, Exp::Ap(target, arg), retType)
 ------------------------------------- {
   Check(ctx, target, Type::Arrow(argType, retType))
   Check(ctx, arg, argType)
diff --git a/docs/langs/lambda-simple-type.ch.out b/docs/examples/langs/lambda-simple-type.ch.out
similarity index 100%
rename from docs/langs/lambda-simple-type.ch.out
rename to docs/examples/langs/lambda-simple-type.ch.out
diff --git a/docs/examples/std/list/Append.ch b/docs/examples/std/list/Append.ch
new file mode 100644
index 00000000..59351a51
--- /dev/null
+++ b/docs/examples/std/list/Append.ch
@@ -0,0 +1,6 @@
+export { Append }
+
+relation Append([], l, l)
+relation Append([a | d], l, [a | r]) -- {
+  Append(d, l, r)
+}
diff --git a/docs/std/list/Append.test.ch b/docs/examples/std/list/Append.test.ch
similarity index 100%
rename from docs/std/list/Append.test.ch
rename to docs/examples/std/list/Append.test.ch
diff --git a/docs/std/list/Append.test.ch.out b/docs/examples/std/list/Append.test.ch.out
similarity index 100%
rename from docs/std/list/Append.test.ch.out
rename to docs/examples/std/list/Append.test.ch.out
diff --git a/docs/std/list/Lookup.ch b/docs/examples/std/list/Lookup.ch
similarity index 79%
rename from docs/std/list/Lookup.ch
rename to docs/examples/std/list/Lookup.ch
index 69017b61..0515e5e3 100644
--- a/docs/std/list/Lookup.ch
+++ b/docs/examples/std/list/Lookup.ch
@@ -1,13 +1,13 @@
 export { Lookup }
 
-clause Lookup(map, name, found)
+relation Lookup(map, name, found)
 ------------------------- here {
   Equal(map, [[key, value] | _rest])
   Equal(key, name)
   Equal(found, value)
 }
 
-clause Lookup(map, name, found)
+relation Lookup(map, name, found)
 ------------------------------- there {
   Equal(map, [[key, _value] | rest])
   NotEqual(key, name)
diff --git a/docs/std/list/Lookup.test.ch b/docs/examples/std/list/Lookup.test.ch
similarity index 100%
rename from docs/std/list/Lookup.test.ch
rename to docs/examples/std/list/Lookup.test.ch
diff --git a/docs/std/list/Lookup.test.ch.out b/docs/examples/std/list/Lookup.test.ch.out
similarity index 100%
rename from docs/std/list/Lookup.test.ch.out
rename to docs/examples/std/list/Lookup.test.ch.out
diff --git a/docs/std/list/index.ch b/docs/examples/std/list/index.ch
similarity index 100%
rename from docs/std/list/index.ch
rename to docs/examples/std/list/index.ch
diff --git a/docs/std/nat/Add.ch b/docs/examples/std/nat/Add.ch
similarity index 57%
rename from docs/std/nat/Add.ch
rename to docs/examples/std/nat/Add.ch
index 4e6c38ca..0201e679 100644
--- a/docs/std/nat/Add.ch
+++ b/docs/examples/std/nat/Add.ch
@@ -2,8 +2,8 @@ import { Zero, Add1, Nat } from "Nat.ch"
 
 export { Add }
 
-clause Add(Nat::Zero(), y, y)
-clause Add(Nat::Add1(prev), y, Nat::Add1(res))
+relation Add(Nat::Zero(), y, y)
+relation Add(Nat::Add1(prev), y, Nat::Add1(res))
 --------------------------- {
   Add(prev, y, res)
 }
diff --git a/docs/std/nat/Add.test.ch b/docs/examples/std/nat/Add.test.ch
similarity index 100%
rename from docs/std/nat/Add.test.ch
rename to docs/examples/std/nat/Add.test.ch
diff --git a/docs/std/nat/Add.test.ch.out b/docs/examples/std/nat/Add.test.ch.out
similarity index 100%
rename from docs/std/nat/Add.test.ch.out
rename to docs/examples/std/nat/Add.test.ch.out
diff --git a/docs/std/nat/Mul.ch b/docs/examples/std/nat/Mul.ch
similarity index 82%
rename from docs/std/nat/Mul.ch
rename to docs/examples/std/nat/Mul.ch
index 1f499b68..cbf810dc 100644
--- a/docs/std/nat/Mul.ch
+++ b/docs/examples/std/nat/Mul.ch
@@ -3,20 +3,20 @@ import { Add } from "Add.ch"
 
 export { Mul }
 
-clause Mul(x, _y, z)
+relation Mul(x, _y, z)
 --------------- zero_left {
   Zero(x)
   Zero(z)
 }
 
-clause Mul(x, y, z)
+relation Mul(x, y, z)
 ----------------- add1_left_zero_right {
   Zero(y)
   Zero(z)
   Add1(_prev, x)
 }
 
-clause Mul(x, y, out)
+relation Mul(x, y, out)
 ----------------- add1_left_add1_right {
   Add1(prev, x)
   Add1(_prev, y)
diff --git a/docs/std/nat/Mul.test.ch b/docs/examples/std/nat/Mul.test.ch
similarity index 100%
rename from docs/std/nat/Mul.test.ch
rename to docs/examples/std/nat/Mul.test.ch
diff --git a/docs/std/nat/Mul.test.ch.out b/docs/examples/std/nat/Mul.test.ch.out
similarity index 100%
rename from docs/std/nat/Mul.test.ch.out
rename to docs/examples/std/nat/Mul.test.ch.out
diff --git a/docs/examples/std/nat/Nat.ch b/docs/examples/std/nat/Nat.ch
new file mode 100644
index 00000000..42b8cd46
--- /dev/null
+++ b/docs/examples/std/nat/Nat.ch
@@ -0,0 +1,7 @@
+export { Nat, Zero, Add1 }
+
+relation Nat(Nat::Zero())
+relation Nat(Nat::Add1(prev)) -- { Nat(prev) }
+
+relation Zero(Nat::Zero())
+relation Add1(prev, Nat::Add1(prev))
diff --git a/docs/std/nat/index.ch b/docs/examples/std/nat/index.ch
similarity index 100%
rename from docs/std/nat/index.ch
rename to docs/examples/std/nat/index.ch
diff --git a/docs/examples/std/nat/numbers.ch b/docs/examples/std/nat/numbers.ch
new file mode 100644
index 00000000..73ff293b
--- /dev/null
+++ b/docs/examples/std/nat/numbers.ch
@@ -0,0 +1,14 @@
+import { Zero, Add1 } from "Nat.ch"
+
+export relation One(n) -- { Add1(prev, n) Zero(prev) }
+export relation Two(n) -- { Add1(prev, n) One(prev) }
+export relation Three(n) -- { Add1(prev, n) Two(prev) }
+export relation Four(n) -- { Add1(prev, n) Three(prev) }
+export relation Five(n) -- { Add1(prev, n) Four(prev) }
+export relation Six(n) -- { Add1(prev, n) Five(prev) }
+export relation Seven(n) -- { Add1(prev, n) Six(prev) }
+export relation Eight(n) -- { Add1(prev, n) Seven(prev) }
+export relation Nine(n) -- { Add1(prev, n) Eight(prev) }
+export relation Ten(n) -- { Add1(prev, n) Nine(prev) }
+export relation Eleven(n) -- { Add1(prev, n) Ten(prev) }
+export relation Twelve(n) -- { Add1(prev, n) Eleven(prev) }
diff --git a/docs/std/nat/play.ch b/docs/examples/std/nat/play.ch
similarity index 94%
rename from docs/std/nat/play.ch
rename to docs/examples/std/nat/play.ch
index c9d6267a..11162628 100644
--- a/docs/std/nat/play.ch
+++ b/docs/examples/std/nat/play.ch
@@ -1,4 +1,4 @@
-clause LtEqThree(n)
+relation LtEqThree(n)
 -------------- {
   NotEqual(n, Nat::Add1(Nat::Add1(Nat::Add1(Nat::Zero()))))
 }
diff --git a/docs/std/nat/play.ch.out b/docs/examples/std/nat/play.ch.out
similarity index 100%
rename from docs/std/nat/play.ch.out
rename to docs/examples/std/nat/play.ch.out
diff --git a/docs/examples/std/trilean/Trilean.ch b/docs/examples/std/trilean/Trilean.ch
new file mode 100644
index 00000000..7a5fc66e
--- /dev/null
+++ b/docs/examples/std/trilean/Trilean.ch
@@ -0,0 +1,62 @@
+// Use logic programming to play with many-valued logic.
+
+relation Trilean(0)
+relation Trilean(0.5)
+relation Trilean(1)
+
+// Name of the three values:
+
+relation TrileanFalse(0)
+relation TrileanMiddle(0.5)
+relation TrileanTrue(1)
+
+relation TrileanMin(0, 0, 0)
+relation TrileanMin(0, 0.5, 0)
+relation TrileanMin(0, 1, 0)
+relation TrileanMin(0.5, 0, 0)
+relation TrileanMin(0.5, 0.5, 0.5)
+relation TrileanMin(0.5, 1, 0.5)
+relation TrileanMin(1, 0, 0)
+relation TrileanMin(1, 0.5, 0.5)
+relation TrileanMin(1, 1, 1)
+
+relation TrileanMax(0, 0, 0)
+relation TrileanMax(0, 0.5, 0.5)
+relation TrileanMax(0, 1, 1)
+relation TrileanMax(0.5, 0, 0.5)
+relation TrileanMax(0.5, 0.5, 0.5)
+relation TrileanMax(0.5, 1, 1)
+relation TrileanMax(1, 0, 1)
+relation TrileanMax(1, 0.5, 1)
+relation TrileanMax(1, 1, 1)
+
+relation TrileanPositive(0.5)
+relation TrileanPositive(1)
+
+// Use mutually exclusive cases.
+
+relation TrileanMul(0, y, 0) -- { Trilean(y) }
+relation TrileanMul(x, 0, 0) -- { TrileanPositive(x) }
+relation TrileanMul(x, y, z) -- {
+  TrileanPositive(x)
+  TrileanPositive(y)
+  TrileanMax(x, y, z)
+}
+
+// See how `TrileanMax` is different from `TrileanMul`:
+
+print find [x, y, z] { TrileanMax(x, y, z) }
+print find [x, y, z] { TrileanMul(x, y, z) }
+
+// What returns 0?
+print find [x, y] { TrileanMul(x, y, 0) }
+
+// [question] Can `TrileansMul` be defined by
+// composition of other connectives (not, min, max)?
+// Does this means to use only one clause?
+
+// [question] How to search high-order things
+// like connective in logic programming?
+// We want to search how to construct truth function
+// by composition of given set of connectives.
+// Maybe we must define first order expressions first.
diff --git a/docs/std/trilean/Trilean.ch.out b/docs/examples/std/trilean/Trilean.ch.out
similarity index 100%
rename from docs/std/trilean/Trilean.ch.out
rename to docs/examples/std/trilean/Trilean.ch.out
diff --git a/docs/tests/basic/assert-false.error.ch b/docs/examples/tests/basic/assert-false.error.ch
similarity index 100%
rename from docs/tests/basic/assert-false.error.ch
rename to docs/examples/tests/basic/assert-false.error.ch
diff --git a/docs/tests/basic/assert-false.error.ch.err b/docs/examples/tests/basic/assert-false.error.ch.err
similarity index 100%
rename from docs/tests/basic/assert-false.error.ch.err
rename to docs/examples/tests/basic/assert-false.error.ch.err
diff --git a/docs/tests/basic/assert-non-boolean.error.ch b/docs/examples/tests/basic/assert-non-boolean.error.ch
similarity index 100%
rename from docs/tests/basic/assert-non-boolean.error.ch
rename to docs/examples/tests/basic/assert-non-boolean.error.ch
diff --git a/docs/tests/basic/assert-non-boolean.error.ch.err b/docs/examples/tests/basic/assert-non-boolean.error.ch.err
similarity index 100%
rename from docs/tests/basic/assert-non-boolean.error.ch.err
rename to docs/examples/tests/basic/assert-non-boolean.error.ch.err
diff --git a/docs/tests/basic/assert.ch b/docs/examples/tests/basic/assert.ch
similarity index 100%
rename from docs/tests/basic/assert.ch
rename to docs/examples/tests/basic/assert.ch
diff --git a/docs/tests/basic/compute.ch b/docs/examples/tests/basic/compute.ch
similarity index 100%
rename from docs/tests/basic/compute.ch
rename to docs/examples/tests/basic/compute.ch
diff --git a/docs/tests/basic/compute.ch.out b/docs/examples/tests/basic/compute.ch.out
similarity index 100%
rename from docs/tests/basic/compute.ch.out
rename to docs/examples/tests/basic/compute.ch.out
diff --git a/docs/tests/basic/currying.ch b/docs/examples/tests/basic/currying.ch
similarity index 100%
rename from docs/tests/basic/currying.ch
rename to docs/examples/tests/basic/currying.ch
diff --git a/docs/tests/basic/currying.ch.out b/docs/examples/tests/basic/currying.ch.out
similarity index 100%
rename from docs/tests/basic/currying.ch.out
rename to docs/examples/tests/basic/currying.ch.out
diff --git a/docs/tests/basic/dot.ch b/docs/examples/tests/basic/dot.ch
similarity index 100%
rename from docs/tests/basic/dot.ch
rename to docs/examples/tests/basic/dot.ch
diff --git a/docs/tests/basic/function-print.ch b/docs/examples/tests/basic/function-print.ch
similarity index 100%
rename from docs/tests/basic/function-print.ch
rename to docs/examples/tests/basic/function-print.ch
diff --git a/docs/tests/basic/function-print.ch.out b/docs/examples/tests/basic/function-print.ch.out
similarity index 100%
rename from docs/tests/basic/function-print.ch.out
rename to docs/examples/tests/basic/function-print.ch.out
diff --git a/docs/tests/basic/function-with-clause.ch b/docs/examples/tests/basic/function-with-clause.ch
similarity index 91%
rename from docs/tests/basic/function-with-clause.ch
rename to docs/examples/tests/basic/function-with-clause.ch
index a6ab2960..5b2e113a 100644
--- a/docs/tests/basic/function-with-clause.ch
+++ b/docs/examples/tests/basic/function-with-clause.ch
@@ -1,5 +1,5 @@
 function greet(x) {
-  clause Hi("hi")
+  relation Hi("hi")
 
   // The expressions in `find` are implicitly `quote`d.
 
diff --git a/docs/tests/basic/function-with-clause.ch.out b/docs/examples/tests/basic/function-with-clause.ch.out
similarity index 100%
rename from docs/tests/basic/function-with-clause.ch.out
rename to docs/examples/tests/basic/function-with-clause.ch.out
diff --git a/docs/tests/basic/function-with-early-return.ch b/docs/examples/tests/basic/function-with-early-return.ch
similarity index 100%
rename from docs/tests/basic/function-with-early-return.ch
rename to docs/examples/tests/basic/function-with-early-return.ch
diff --git a/docs/tests/basic/function-with-early-return.ch.out b/docs/examples/tests/basic/function-with-early-return.ch.out
similarity index 100%
rename from docs/tests/basic/function-with-early-return.ch.out
rename to docs/examples/tests/basic/function-with-early-return.ch.out
diff --git a/docs/tests/basic/function-with-return-expression.ch b/docs/examples/tests/basic/function-with-return-expression.ch
similarity index 100%
rename from docs/tests/basic/function-with-return-expression.ch
rename to docs/examples/tests/basic/function-with-return-expression.ch
diff --git a/docs/tests/basic/function-with-return-expression.ch.out b/docs/examples/tests/basic/function-with-return-expression.ch.out
similarity index 100%
rename from docs/tests/basic/function-with-return-expression.ch.out
rename to docs/examples/tests/basic/function-with-return-expression.ch.out
diff --git a/docs/tests/basic/function-with-return-null.ch b/docs/examples/tests/basic/function-with-return-null.ch
similarity index 100%
rename from docs/tests/basic/function-with-return-null.ch
rename to docs/examples/tests/basic/function-with-return-null.ch
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similarity index 100%
rename from docs/tests/basic/function-with-return-null.ch.out
rename to docs/examples/tests/basic/function-with-return-null.ch.out
diff --git a/docs/tests/basic/function.ch b/docs/examples/tests/basic/function.ch
similarity index 100%
rename from docs/tests/basic/function.ch
rename to docs/examples/tests/basic/function.ch
diff --git a/docs/tests/basic/function.ch.out b/docs/examples/tests/basic/function.ch.out
similarity index 100%
rename from docs/tests/basic/function.ch.out
rename to docs/examples/tests/basic/function.ch.out
diff --git a/docs/tests/basic/if-else-if.ch b/docs/examples/tests/basic/if-else-if.ch
similarity index 100%
rename from docs/tests/basic/if-else-if.ch
rename to docs/examples/tests/basic/if-else-if.ch
diff --git a/docs/tests/basic/if-else-if.ch.out b/docs/examples/tests/basic/if-else-if.ch.out
similarity index 100%
rename from docs/tests/basic/if-else-if.ch.out
rename to docs/examples/tests/basic/if-else-if.ch.out
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similarity index 100%
rename from docs/tests/basic/if-exp-without-else.ch
rename to docs/examples/tests/basic/if-exp-without-else.ch
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similarity index 100%
rename from docs/tests/basic/if-exp-without-else.ch.out
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similarity index 100%
rename from docs/tests/basic/if-exp.ch
rename to docs/examples/tests/basic/if-exp.ch
diff --git a/docs/tests/basic/if-exp.ch.out b/docs/examples/tests/basic/if-exp.ch.out
similarity index 100%
rename from docs/tests/basic/if-exp.ch.out
rename to docs/examples/tests/basic/if-exp.ch.out
diff --git a/docs/tests/basic/if-non-boolean-target.error.ch b/docs/examples/tests/basic/if-non-boolean-target.error.ch
similarity index 100%
rename from docs/tests/basic/if-non-boolean-target.error.ch
rename to docs/examples/tests/basic/if-non-boolean-target.error.ch
diff --git a/docs/tests/basic/if-non-boolean-target.error.ch.err b/docs/examples/tests/basic/if-non-boolean-target.error.ch.err
similarity index 100%
rename from docs/tests/basic/if-non-boolean-target.error.ch.err
rename to docs/examples/tests/basic/if-non-boolean-target.error.ch.err
diff --git a/docs/tests/basic/if-without-else.ch b/docs/examples/tests/basic/if-without-else.ch
similarity index 100%
rename from docs/tests/basic/if-without-else.ch
rename to docs/examples/tests/basic/if-without-else.ch
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similarity index 100%
rename from docs/tests/basic/if-without-else.ch.out
rename to docs/examples/tests/basic/if-without-else.ch.out
diff --git a/docs/tests/basic/if.ch b/docs/examples/tests/basic/if.ch
similarity index 100%
rename from docs/tests/basic/if.ch
rename to docs/examples/tests/basic/if.ch
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similarity index 100%
rename from docs/tests/basic/if.ch.out
rename to docs/examples/tests/basic/if.ch.out
diff --git a/docs/tests/basic/let.ch b/docs/examples/tests/basic/let.ch
similarity index 100%
rename from docs/tests/basic/let.ch
rename to docs/examples/tests/basic/let.ch
diff --git a/docs/tests/basic/print.ch b/docs/examples/tests/basic/print.ch
similarity index 100%
rename from docs/tests/basic/print.ch
rename to docs/examples/tests/basic/print.ch
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similarity index 100%
rename from docs/tests/basic/print.ch.out
rename to docs/examples/tests/basic/print.ch.out
diff --git a/docs/tests/constraints/not-equal.ch b/docs/examples/tests/constraints/not-equal.ch
similarity index 100%
rename from docs/tests/constraints/not-equal.ch
rename to docs/examples/tests/constraints/not-equal.ch
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similarity index 100%
rename from docs/tests/constraints/not-equal.ch.out
rename to docs/examples/tests/constraints/not-equal.ch.out
diff --git a/docs/tests/constraints/number-types.ch b/docs/examples/tests/constraints/number-types.ch
similarity index 100%
rename from docs/tests/constraints/number-types.ch
rename to docs/examples/tests/constraints/number-types.ch
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similarity index 100%
rename from docs/tests/constraints/number-types.ch.out
rename to docs/examples/tests/constraints/number-types.ch.out
diff --git a/docs/tests/constraints/string-types.ch b/docs/examples/tests/constraints/string-types.ch
similarity index 100%
rename from docs/tests/constraints/string-types.ch
rename to docs/examples/tests/constraints/string-types.ch
diff --git a/docs/tests/constraints/string-types.ch.out b/docs/examples/tests/constraints/string-types.ch.out
similarity index 100%
rename from docs/tests/constraints/string-types.ch.out
rename to docs/examples/tests/constraints/string-types.ch.out
diff --git a/docs/tests/conventions/no-misused-variable-name.error.ch b/docs/examples/tests/conventions/no-misused-variable-name.error.ch
similarity index 64%
rename from docs/tests/conventions/no-misused-variable-name.error.ch
rename to docs/examples/tests/conventions/no-misused-variable-name.error.ch
index e8f957dc..de4bd6c9 100644
--- a/docs/tests/conventions/no-misused-variable-name.error.ch
+++ b/docs/examples/tests/conventions/no-misused-variable-name.error.ch
@@ -1,4 +1,4 @@
-clause Car(p, _a)
+relation Car(p, _a)
 ---------- {
   Equal([_a | _d], p)
 }
diff --git a/docs/tests/conventions/no-misused-variable-name.error.ch.err b/docs/examples/tests/conventions/no-misused-variable-name.error.ch.err
similarity index 92%
rename from docs/tests/conventions/no-misused-variable-name.error.ch.err
rename to docs/examples/tests/conventions/no-misused-variable-name.error.ch.err
index 514312c3..3949f27c 100644
--- a/docs/tests/conventions/no-misused-variable-name.error.ch.err
+++ b/docs/examples/tests/conventions/no-misused-variable-name.error.ch.err
@@ -2,6 +2,6 @@
   pattern variable name: _a
 [note] This policy about unused pattern variable name is important for finding bugs caused by typo.
 
- 1 |clause Car(p, _a)
+ 1 |relation Car(p, _a)
  2 |---------- {
  3 |  Equal([_a | _d], p)
diff --git a/docs/tests/conventions/no-unused-variable-name.error.ch b/docs/examples/tests/conventions/no-unused-variable-name.error.ch
similarity index 64%
rename from docs/tests/conventions/no-unused-variable-name.error.ch
rename to docs/examples/tests/conventions/no-unused-variable-name.error.ch
index d0ef9e6b..98e82787 100644
--- a/docs/tests/conventions/no-unused-variable-name.error.ch
+++ b/docs/examples/tests/conventions/no-unused-variable-name.error.ch
@@ -1,4 +1,4 @@
-clause Car(p, a)
+relation Car(p, a)
 ---------- {
   Equal([a | d], p)
 }
diff --git a/docs/tests/conventions/no-unused-variable-name.error.ch.err b/docs/examples/tests/conventions/no-unused-variable-name.error.ch.err
similarity index 92%
rename from docs/tests/conventions/no-unused-variable-name.error.ch.err
rename to docs/examples/tests/conventions/no-unused-variable-name.error.ch.err
index 81b4d136..4636d213 100644
--- a/docs/tests/conventions/no-unused-variable-name.error.ch.err
+++ b/docs/examples/tests/conventions/no-unused-variable-name.error.ch.err
@@ -2,7 +2,7 @@
   pattern variable name: d
 [note] This policy about unused pattern variable name is important for finding bugs caused by typo.
 
- 1 |clause Car(p, a)
+ 1 |relation Car(p, a)
  2 |---------- {
  3 |  Equal([a | d], p)
  4 |}
diff --git a/docs/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch b/docs/examples/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch
similarity index 100%
rename from docs/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch
rename to docs/examples/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch
diff --git a/docs/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch.out b/docs/examples/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch.out
similarity index 100%
rename from docs/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch.out
rename to docs/examples/tests/conventions/pattern-variable-name-can-starts-with-uppercase.ch.out
diff --git a/docs/tests/conventions/preserved-name-false.error.ch b/docs/examples/tests/conventions/preserved-name-false.error.ch
similarity index 100%
rename from docs/tests/conventions/preserved-name-false.error.ch
rename to docs/examples/tests/conventions/preserved-name-false.error.ch
diff --git a/docs/tests/conventions/preserved-name-false.error.ch.err b/docs/examples/tests/conventions/preserved-name-false.error.ch.err
similarity index 100%
rename from docs/tests/conventions/preserved-name-false.error.ch.err
rename to docs/examples/tests/conventions/preserved-name-false.error.ch.err
diff --git a/docs/tests/conventions/preserved-name-null.error.ch b/docs/examples/tests/conventions/preserved-name-null.error.ch
similarity index 100%
rename from docs/tests/conventions/preserved-name-null.error.ch
rename to docs/examples/tests/conventions/preserved-name-null.error.ch
diff --git a/docs/tests/conventions/preserved-name-null.error.ch.err b/docs/examples/tests/conventions/preserved-name-null.error.ch.err
similarity index 100%
rename from docs/tests/conventions/preserved-name-null.error.ch.err
rename to docs/examples/tests/conventions/preserved-name-null.error.ch.err
diff --git a/docs/tests/conventions/preserved-name-true.error.ch b/docs/examples/tests/conventions/preserved-name-true.error.ch
similarity index 100%
rename from docs/tests/conventions/preserved-name-true.error.ch
rename to docs/examples/tests/conventions/preserved-name-true.error.ch
diff --git a/docs/tests/conventions/preserved-name-true.error.ch.err b/docs/examples/tests/conventions/preserved-name-true.error.ch.err
similarity index 100%
rename from docs/tests/conventions/preserved-name-true.error.ch.err
rename to docs/examples/tests/conventions/preserved-name-true.error.ch.err
diff --git a/docs/examples/tests/conventions/relation-arity-mismatch.error.ch b/docs/examples/tests/conventions/relation-arity-mismatch.error.ch
new file mode 100644
index 00000000..9d3403ea
--- /dev/null
+++ b/docs/examples/tests/conventions/relation-arity-mismatch.error.ch
@@ -0,0 +1,2 @@
+relation F(1)
+relation F(1, 2)
diff --git a/docs/tests/conventions/relation-arity-mismatch.error.ch.err b/docs/examples/tests/conventions/relation-arity-mismatch.error.ch.err
similarity index 100%
rename from docs/tests/conventions/relation-arity-mismatch.error.ch.err
rename to docs/examples/tests/conventions/relation-arity-mismatch.error.ch.err
diff --git a/docs/examples/tests/conventions/relation-name-must-starts-with-uppercase.error.ch b/docs/examples/tests/conventions/relation-name-must-starts-with-uppercase.error.ch
new file mode 100644
index 00000000..6d89dc44
--- /dev/null
+++ b/docs/examples/tests/conventions/relation-name-must-starts-with-uppercase.error.ch
@@ -0,0 +1 @@
+relation border("sussex", "kent")
diff --git a/docs/examples/tests/conventions/relation-name-must-starts-with-uppercase.error.ch.err b/docs/examples/tests/conventions/relation-name-must-starts-with-uppercase.error.ch.err
new file mode 100644
index 00000000..f00c2803
--- /dev/null
+++ b/docs/examples/tests/conventions/relation-name-must-starts-with-uppercase.error.ch.err
@@ -0,0 +1,14 @@
+I found syntax error in code:
+
+ 1 |relation border("sussex", "kent")
+ 2 |
+
+
+Found the identifier "border" in [9, 15], while expecting:
+ ["identifier"]:
+     stmt:clause_no_goals_no_name@0 -> "relation"@1 > (name: identifier) (args: args) 
+ ["identifier"]:
+     stmt:clause_no_goals@0 -> "relation"@1 > (name: identifier) (args: args) dashline (clause_name: identifier) 
+ ["identifier"]:
+     stmt:clause_no_name@0 -> "relation"@1 > (name: identifier) (args: args) dashline "{" (goals: goals) "}" 
+ and so on ...
diff --git a/docs/tests/globals/boolean.ch b/docs/examples/tests/globals/boolean.ch
similarity index 100%
rename from docs/tests/globals/boolean.ch
rename to docs/examples/tests/globals/boolean.ch
diff --git a/docs/tests/globals/boolean.ch.out b/docs/examples/tests/globals/boolean.ch.out
similarity index 100%
rename from docs/tests/globals/boolean.ch.out
rename to docs/examples/tests/globals/boolean.ch.out
diff --git a/docs/tests/globals/equal.ch b/docs/examples/tests/globals/equal.ch
similarity index 100%
rename from docs/tests/globals/equal.ch
rename to docs/examples/tests/globals/equal.ch
diff --git a/docs/tests/globals/equal.ch.out b/docs/examples/tests/globals/equal.ch.out
similarity index 100%
rename from docs/tests/globals/equal.ch.out
rename to docs/examples/tests/globals/equal.ch.out
diff --git a/docs/tests/globals/not-equal.ch b/docs/examples/tests/globals/not-equal.ch
similarity index 100%
rename from docs/tests/globals/not-equal.ch
rename to docs/examples/tests/globals/not-equal.ch
diff --git a/docs/tests/globals/not-equal.ch.out b/docs/examples/tests/globals/not-equal.ch.out
similarity index 100%
rename from docs/tests/globals/not-equal.ch.out
rename to docs/examples/tests/globals/not-equal.ch.out
diff --git a/docs/tests/globals/null-shadowed.ch b/docs/examples/tests/globals/null-shadowed.ch
similarity index 57%
rename from docs/tests/globals/null-shadowed.ch
rename to docs/examples/tests/globals/null-shadowed.ch
index 71a23470..f07d7b59 100644
--- a/docs/tests/globals/null-shadowed.ch
+++ b/docs/examples/tests/globals/null-shadowed.ch
@@ -2,7 +2,7 @@ print find x {
   Null(x)
 }
 
-clause Null(x) -- { Equal(x, "null") }
+relation Null(x) -- { Equal(x, "null") }
 
 print find x {
   Null(x)
diff --git a/docs/tests/globals/null-shadowed.ch.out b/docs/examples/tests/globals/null-shadowed.ch.out
similarity index 100%
rename from docs/tests/globals/null-shadowed.ch.out
rename to docs/examples/tests/globals/null-shadowed.ch.out
diff --git a/docs/tests/globals/null.ch b/docs/examples/tests/globals/null.ch
similarity index 100%
rename from docs/tests/globals/null.ch
rename to docs/examples/tests/globals/null.ch
diff --git a/docs/tests/globals/null.ch.out b/docs/examples/tests/globals/null.ch.out
similarity index 100%
rename from docs/tests/globals/null.ch.out
rename to docs/examples/tests/globals/null.ch.out
diff --git a/docs/tests/goal/goal-apply-too-many-arguments.error.ch b/docs/examples/tests/goal/goal-apply-too-many-arguments.error.ch
similarity index 100%
rename from docs/tests/goal/goal-apply-too-many-arguments.error.ch
rename to docs/examples/tests/goal/goal-apply-too-many-arguments.error.ch
diff --git a/docs/tests/goal/goal-apply-too-many-arguments.error.ch.err b/docs/examples/tests/goal/goal-apply-too-many-arguments.error.ch.err
similarity index 100%
rename from docs/tests/goal/goal-apply-too-many-arguments.error.ch.err
rename to docs/examples/tests/goal/goal-apply-too-many-arguments.error.ch.err
diff --git a/docs/tests/goal/goal.ch b/docs/examples/tests/goal/goal.ch
similarity index 100%
rename from docs/tests/goal/goal.ch
rename to docs/examples/tests/goal/goal.ch
diff --git a/docs/tests/goal/goal.ch.out b/docs/examples/tests/goal/goal.ch.out
similarity index 100%
rename from docs/tests/goal/goal.ch.out
rename to docs/examples/tests/goal/goal.ch.out
diff --git a/docs/tests/json/array.ch b/docs/examples/tests/json/array.ch
similarity index 100%
rename from docs/tests/json/array.ch
rename to docs/examples/tests/json/array.ch
diff --git a/docs/tests/json/array.ch.out b/docs/examples/tests/json/array.ch.out
similarity index 100%
rename from docs/tests/json/array.ch.out
rename to docs/examples/tests/json/array.ch.out
diff --git a/docs/tests/json/boolean.ch b/docs/examples/tests/json/boolean.ch
similarity index 100%
rename from docs/tests/json/boolean.ch
rename to docs/examples/tests/json/boolean.ch
diff --git a/docs/tests/json/boolean.ch.out b/docs/examples/tests/json/boolean.ch.out
similarity index 100%
rename from docs/tests/json/boolean.ch.out
rename to docs/examples/tests/json/boolean.ch.out
diff --git a/docs/tests/json/null.ch b/docs/examples/tests/json/null.ch
similarity index 100%
rename from docs/tests/json/null.ch
rename to docs/examples/tests/json/null.ch
diff --git a/docs/tests/json/null.ch.out b/docs/examples/tests/json/null.ch.out
similarity index 100%
rename from docs/tests/json/null.ch.out
rename to docs/examples/tests/json/null.ch.out
diff --git a/docs/tests/json/number.ch b/docs/examples/tests/json/number.ch
similarity index 100%
rename from docs/tests/json/number.ch
rename to docs/examples/tests/json/number.ch
diff --git a/docs/tests/json/number.ch.out b/docs/examples/tests/json/number.ch.out
similarity index 100%
rename from docs/tests/json/number.ch.out
rename to docs/examples/tests/json/number.ch.out
diff --git a/docs/tests/json/object.ch b/docs/examples/tests/json/object.ch
similarity index 100%
rename from docs/tests/json/object.ch
rename to docs/examples/tests/json/object.ch
diff --git a/docs/tests/json/object.ch.out b/docs/examples/tests/json/object.ch.out
similarity index 100%
rename from docs/tests/json/object.ch.out
rename to docs/examples/tests/json/object.ch.out
diff --git a/docs/tests/json/string.ch b/docs/examples/tests/json/string.ch
similarity index 100%
rename from docs/tests/json/string.ch
rename to docs/examples/tests/json/string.ch
diff --git a/docs/tests/json/string.ch.out b/docs/examples/tests/json/string.ch.out
similarity index 100%
rename from docs/tests/json/string.ch.out
rename to docs/examples/tests/json/string.ch.out
diff --git a/docs/tests/module/A.ch b/docs/examples/tests/module/A.ch
similarity index 72%
rename from docs/tests/module/A.ch
rename to docs/examples/tests/module/A.ch
index f5e1ee32..42ea7bb4 100644
--- a/docs/tests/module/A.ch
+++ b/docs/examples/tests/module/A.ch
@@ -1,4 +1,4 @@
-export clause A(a)
+export relation A(a)
 ------ {
   Equal(a, "a")
 }
diff --git a/docs/tests/module/A.ch.out b/docs/examples/tests/module/A.ch.out
similarity index 100%
rename from docs/tests/module/A.ch.out
rename to docs/examples/tests/module/A.ch.out
diff --git a/docs/tests/module/AB.ch b/docs/examples/tests/module/AB.ch
similarity index 80%
rename from docs/tests/module/AB.ch
rename to docs/examples/tests/module/AB.ch
index f85e6d36..23b90d5b 100644
--- a/docs/tests/module/AB.ch
+++ b/docs/examples/tests/module/AB.ch
@@ -1,6 +1,6 @@
 import { A } from "./A.ch"
 
-export clause AB(a, b)
+export relation AB(a, b)
 ---------- {
   A(a)
   Equal(b, "b")
diff --git a/docs/tests/module/AB.ch.out b/docs/examples/tests/module/AB.ch.out
similarity index 100%
rename from docs/tests/module/AB.ch.out
rename to docs/examples/tests/module/AB.ch.out
diff --git a/docs/tests/module/ABC.ch b/docs/examples/tests/module/ABC.ch
similarity index 80%
rename from docs/tests/module/ABC.ch
rename to docs/examples/tests/module/ABC.ch
index f88459d3..64a59beb 100644
--- a/docs/tests/module/ABC.ch
+++ b/docs/examples/tests/module/ABC.ch
@@ -1,6 +1,6 @@
 import { AB } from "./AB.ch"
 
-export clause ABC(a, b, c)
+export relation ABC(a, b, c)
 -------------- {
   AB(a, b)
   Equal(c, "c")
diff --git a/docs/tests/module/ABC.ch.out b/docs/examples/tests/module/ABC.ch.out
similarity index 100%
rename from docs/tests/module/ABC.ch.out
rename to docs/examples/tests/module/ABC.ch.out
diff --git a/docs/examples/tests/module/example.ch b/docs/examples/tests/module/example.ch
new file mode 100644
index 00000000..052b5c4e
--- /dev/null
+++ b/docs/examples/tests/module/example.ch
@@ -0,0 +1,5 @@
+export relation Hello("Hello, World!")
+
+export relation Hi("Hi there!")
+
+relation Hiya("Hiya!")
diff --git a/docs/tests/module/import-all-as.ch b/docs/examples/tests/module/import-all-as.ch
similarity index 100%
rename from docs/tests/module/import-all-as.ch
rename to docs/examples/tests/module/import-all-as.ch
diff --git a/docs/tests/module/import-all-as.ch.out b/docs/examples/tests/module/import-all-as.ch.out
similarity index 100%
rename from docs/tests/module/import-all-as.ch.out
rename to docs/examples/tests/module/import-all-as.ch.out
diff --git a/docs/tests/module/import-all-private.error.ch b/docs/examples/tests/module/import-all-private.error.ch
similarity index 100%
rename from docs/tests/module/import-all-private.error.ch
rename to docs/examples/tests/module/import-all-private.error.ch
diff --git a/docs/tests/module/import-all-private.error.ch.err b/docs/examples/tests/module/import-all-private.error.ch.err
similarity index 100%
rename from docs/tests/module/import-all-private.error.ch.err
rename to docs/examples/tests/module/import-all-private.error.ch.err
diff --git a/docs/tests/module/import-all.ch b/docs/examples/tests/module/import-all.ch
similarity index 100%
rename from docs/tests/module/import-all.ch
rename to docs/examples/tests/module/import-all.ch
diff --git a/docs/tests/module/import-all.ch.out b/docs/examples/tests/module/import-all.ch.out
similarity index 100%
rename from docs/tests/module/import-all.ch.out
rename to docs/examples/tests/module/import-all.ch.out
diff --git a/docs/tests/module/import-private.error.ch b/docs/examples/tests/module/import-private.error.ch
similarity index 100%
rename from docs/tests/module/import-private.error.ch
rename to docs/examples/tests/module/import-private.error.ch
diff --git a/docs/tests/module/import-private.error.ch.err b/docs/examples/tests/module/import-private.error.ch.err
similarity index 100%
rename from docs/tests/module/import-private.error.ch.err
rename to docs/examples/tests/module/import-private.error.ch.err
diff --git a/docs/tests/module/imported-name-can-be-shadowed.ch b/docs/examples/tests/module/imported-name-can-be-shadowed.ch
similarity index 84%
rename from docs/tests/module/imported-name-can-be-shadowed.ch
rename to docs/examples/tests/module/imported-name-can-be-shadowed.ch
index da90cbba..f8b15f14 100644
--- a/docs/tests/module/imported-name-can-be-shadowed.ch
+++ b/docs/examples/tests/module/imported-name-can-be-shadowed.ch
@@ -4,7 +4,7 @@ print find [x] {
   A(x)
 }
 
-clause A(x) -- {
+relation A(x) -- {
   Equal(x, "b")
 }
 
diff --git a/docs/tests/module/imported-name-can-be-shadowed.ch.out b/docs/examples/tests/module/imported-name-can-be-shadowed.ch.out
similarity index 100%
rename from docs/tests/module/imported-name-can-be-shadowed.ch.out
rename to docs/examples/tests/module/imported-name-can-be-shadowed.ch.out
diff --git a/docs/tests/object/construct-object-by-relation.ch b/docs/examples/tests/object/construct-object-by-relation.ch
similarity index 82%
rename from docs/tests/object/construct-object-by-relation.ch
rename to docs/examples/tests/object/construct-object-by-relation.ch
index 0f5cc4d1..3f966db9 100644
--- a/docs/tests/object/construct-object-by-relation.ch
+++ b/docs/examples/tests/object/construct-object-by-relation.ch
@@ -1,4 +1,4 @@
-clause Var(exp, name)
+relation Var(exp, name)
 --------------- {
   Equal(exp, { "@type": "Exp", "@kind": "Var", name })
 }
diff --git a/docs/tests/object/construct-object-by-relation.ch.out b/docs/examples/tests/object/construct-object-by-relation.ch.out
similarity index 100%
rename from docs/tests/object/construct-object-by-relation.ch.out
rename to docs/examples/tests/object/construct-object-by-relation.ch.out
diff --git a/docs/tests/object/merge-properties-to-object.ch b/docs/examples/tests/object/merge-properties-to-object.ch
similarity index 100%
rename from docs/tests/object/merge-properties-to-object.ch
rename to docs/examples/tests/object/merge-properties-to-object.ch
diff --git a/docs/tests/object/merge-properties-to-object.ch.out b/docs/examples/tests/object/merge-properties-to-object.ch.out
similarity index 100%
rename from docs/tests/object/merge-properties-to-object.ch.out
rename to docs/examples/tests/object/merge-properties-to-object.ch.out
diff --git a/docs/tests/relation/conj.ch b/docs/examples/tests/relation/conj.ch
similarity index 100%
rename from docs/tests/relation/conj.ch
rename to docs/examples/tests/relation/conj.ch
diff --git a/docs/tests/relation/conj.ch.out b/docs/examples/tests/relation/conj.ch.out
similarity index 100%
rename from docs/tests/relation/conj.ch.out
rename to docs/examples/tests/relation/conj.ch.out
diff --git a/docs/examples/tests/relation/datom.ch b/docs/examples/tests/relation/datom.ch
new file mode 100644
index 00000000..7436bd84
--- /dev/null
+++ b/docs/examples/tests/relation/datom.ch
@@ -0,0 +1,9 @@
+relation Datom(1, "name", "A")
+relation Datom(1, "age", 45)
+relation Datom(2, "name", "X")
+relation Datom(2, "age", 2)
+
+print find n {
+  Datom(e, "age", 2)
+  Datom(e, "name", n)
+}
diff --git a/docs/tests/relation/datom.ch.out b/docs/examples/tests/relation/datom.ch.out
similarity index 100%
rename from docs/tests/relation/datom.ch.out
rename to docs/examples/tests/relation/datom.ch.out
diff --git a/docs/tests/relation/disj.ch b/docs/examples/tests/relation/disj.ch
similarity index 100%
rename from docs/tests/relation/disj.ch
rename to docs/examples/tests/relation/disj.ch
diff --git a/docs/tests/relation/disj.ch.out b/docs/examples/tests/relation/disj.ch.out
similarity index 100%
rename from docs/tests/relation/disj.ch.out
rename to docs/examples/tests/relation/disj.ch.out
diff --git a/docs/tests/relation/lookup-inline-disj.ch b/docs/examples/tests/relation/lookup-inline-disj.ch
similarity index 88%
rename from docs/tests/relation/lookup-inline-disj.ch
rename to docs/examples/tests/relation/lookup-inline-disj.ch
index 1361c594..b1673912 100644
--- a/docs/tests/relation/lookup-inline-disj.ch
+++ b/docs/examples/tests/relation/lookup-inline-disj.ch
@@ -1,11 +1,11 @@
-clause Lookup(map, name, found)
+relation Lookup(map, name, found)
 ------------------------- here {
   Equal(map, [[key, value] | _rest])
   Equal(key, name)
   Equal(found, value)
 }
 
-clause Lookup(map, name, found)
+relation Lookup(map, name, found)
 ------------------------------- there {
   Equal(map, [[key, _value] | rest])
   NotEqual(key, name)
@@ -24,7 +24,7 @@ print find map limit 3 {
 // TODO We need to improve our search strategy
 // to make the following perform the same as the above.
 
-clause LookupInlinedisj(map, name, found)
+relation LookupInlinedisj(map, name, found)
 ------------------------------------ {
   Equal(map, [[key, value] | rest])
   disj {
diff --git a/docs/tests/relation/lookup-inline-disj.ch.out b/docs/examples/tests/relation/lookup-inline-disj.ch.out
similarity index 100%
rename from docs/tests/relation/lookup-inline-disj.ch.out
rename to docs/examples/tests/relation/lookup-inline-disj.ch.out
diff --git a/docs/tests/relation/multiset-arithmetic.ch b/docs/examples/tests/relation/multiset-arithmetic.ch
similarity index 64%
rename from docs/tests/relation/multiset-arithmetic.ch
rename to docs/examples/tests/relation/multiset-arithmetic.ch
index 294ad572..e57602d2 100644
--- a/docs/tests/relation/multiset-arithmetic.ch
+++ b/docs/examples/tests/relation/multiset-arithmetic.ch
@@ -1,47 +1,47 @@
 // "A multiset approach to arithmetic"
 // https://www.youtube.com/watch?v=4xoF2SRp194
 
-clause Multiset([])
-clause Multiset([car | cdr]) -- { Multiset(car) Multiset(cdr) }
+relation Multiset([])
+relation Multiset([car | cdr]) -- { Multiset(car) Multiset(cdr) }
 
 // print find x limit 10 {
 //   Multiset(x)
 // }
 
-clause Zero([])
+relation Zero([])
 
-clause Nat([])
-clause Nat([car | cdr]) -- { Zero(car) Nat(cdr) }
+relation Nat([])
+relation Nat([car | cdr]) -- { Zero(car) Nat(cdr) }
 
 // print find x limit 10 {
 //   Nat(x)
 // }
 
-clause Poly([])
-clause Poly([car | cdr]) -- { Nat(car) Poly(cdr) }
+relation Poly([])
+relation Poly([car | cdr]) -- { Nat(car) Poly(cdr) }
 
 // print find x limit 10 {
 //   Poly(x)
 // }
 
-clause Multi([])
-clause Multi([car | cdr]) -- { Poly(car) Multi(cdr) }
+relation Multi([])
+relation Multi([car | cdr]) -- { Poly(car) Multi(cdr) }
 
 // print find x limit 10 {
 //   Multi(x)
 // }
 
-clause Append([], t, t)
-clause Append([a | d], t, out) -- {
+relation Append([], t, t)
+relation Append([a | d], t, out) -- {
   Equal(out, [a | res])
   Append(d, t, res)
 }
 
-clause Add(x, y, z) -- { Append(x, y, z) }
+relation Add(x, y, z) -- { Append(x, y, z) }
 
-clause AddMany([], [])
-clause AddMany([x], x)
-clause AddMany([x, y | rest], out) -- {
+relation AddMany([], [])
+relation AddMany([x], x)
+relation AddMany([x, y | rest], out) -- {
   Add(x, y, z)
   AddMany([z | rest], out)
 }
@@ -57,9 +57,9 @@ clause AddMany([x, y | rest], out) -- {
 //   AddMany(xs, out)
 // }
 
-clause Product([], _, [])
-clause Product([_x | _xs], [], [])
-clause Product([x | xs], [y | ys], out) -- {
+relation Product([], _, [])
+relation Product([_x | _xs], [], [])
+relation Product([x | xs], [y | ys], out) -- {
   Product([x], ys, xSide)
   Product(xs, [y], ySide)
   Product(xs, ys, body)
@@ -80,13 +80,13 @@ print find q {
   Product([1, 2, 3], ["a", "b", "c"], q)
 }
 
-clause AddPairs([], [])
-clause AddPairs([[x, y] | ps], [z | res]) -- {
+relation AddPairs([], [])
+relation AddPairs([[x, y] | ps], [z | res]) -- {
   Add(x, y, z)
   AddPairs(ps, res)
 }
 
-clause Mul(x, y, z) -- {
+relation Mul(x, y, z) -- {
   Product(x, y, pairs)
   AddPairs(pairs, z)
 }
@@ -105,9 +105,9 @@ print find [x, y, z] limit 10 {
   Mul(x, y, z)
 }
 
-clause MulMany([], [])
-clause MulMany([x], x)
-clause MulMany([x, y | rest], out) -- {
+relation MulMany([], [])
+relation MulMany([x], x)
+relation MulMany([x, y | rest], out) -- {
   Mul(x, y, z)
   MulMany([z | rest], out)
 }
diff --git a/docs/tests/relation/multiset-arithmetic.ch.out b/docs/examples/tests/relation/multiset-arithmetic.ch.out
similarity index 100%
rename from docs/tests/relation/multiset-arithmetic.ch.out
rename to docs/examples/tests/relation/multiset-arithmetic.ch.out
diff --git a/docs/tests/relation/sat-clause.ch b/docs/examples/tests/relation/sat-clause.ch
similarity index 60%
rename from docs/tests/relation/sat-clause.ch
rename to docs/examples/tests/relation/sat-clause.ch
index 5b76b8d6..f759215e 100644
--- a/docs/tests/relation/sat-clause.ch
+++ b/docs/examples/tests/relation/sat-clause.ch
@@ -2,25 +2,25 @@
 // for `false` and `true`,
 // because the code looks tidier.
 
-clause Bit(x) -- { Equal(x, 0) }
-clause Bit(x) -- { Equal(x, 1) }
+relation Bit(x) -- { Equal(x, 0) }
+relation Bit(x) -- { Equal(x, 1) }
 
-clause Not(0, 1)
-clause Not(1, 0)
+relation Not(0, 1)
+relation Not(1, 0)
 
-clause Or(0, 0, 0)
-clause Or(0, 1, 1)
-clause Or(1, 0, 1)
-clause Or(1, 1, 1)
+relation Or(0, 0, 0)
+relation Or(0, 1, 1)
+relation Or(1, 0, 1)
+relation Or(1, 1, 1)
 
-clause BitList([])
-clause BitList([car | cdr]) -- {
+relation BitList([])
+relation BitList([car | cdr]) -- {
   Bit(car)
   BitList(cdr)
 }
 
-clause ListNot([], [])
-clause ListNot([x | xs], [y | ys]) -- {
+relation ListNot([], [])
+relation ListNot([x | xs], [y | ys]) -- {
   Not(x, y)
   ListNot(xs, ys)
 }
@@ -30,7 +30,7 @@ clause ListNot([x | xs], [y | ys]) -- {
 // which is equivalent to disjunction from
 //   c1 ∨ c2 ∨ ... ¬p1 ∨ ¬p2 ∨ ...
 
-clause Clause(conclusions, premises) -- {
+relation Clause(conclusions, premises) -- {
   BitList(conclusions)
   BitList(premises)
   ListNot(premises, negPremises)
@@ -41,13 +41,13 @@ clause Clause(conclusions, premises) -- {
   ContainsOne(disjunction)
 }
 
-clause ContainsOne([1 | _rest])
-clause ContainsOne([0 | rest]) -- {
+relation ContainsOne([1 | _rest])
+relation ContainsOne([0 | rest]) -- {
   ContainsOne(rest)
 }
 
-clause Append([], t, t)
-clause Append([a | d], t, [a | res]) -- {
+relation Append([], t, t)
+relation Append([a | d], t, [a | res]) -- {
   Append(d, t, res)
 }
 
diff --git a/docs/tests/relation/sat-clause.ch.out b/docs/examples/tests/relation/sat-clause.ch.out
similarity index 100%
rename from docs/tests/relation/sat-clause.ch.out
rename to docs/examples/tests/relation/sat-clause.ch.out
diff --git a/docs/examples/tests/relation/sequencing-of-procedure-calls.ch b/docs/examples/tests/relation/sequencing-of-procedure-calls.ch
new file mode 100644
index 00000000..5702fcf1
--- /dev/null
+++ b/docs/examples/tests/relation/sequencing-of-procedure-calls.ch
@@ -0,0 +1,35 @@
+// Example taken from Robert Kowalski's paper
+// "Predicate logic as a programming language"
+// Chapter "11. SEQUENCING OF PROCEDURE CALLS"
+
+// The point is that doing `Ord` before `Perm`
+// is more efficient.
+
+// relation Sort(x, y) -- s1 { Perm(x, y) Ord(y) }
+relation Sort(x, y) -- s1 { Ord(y) Perm(x, y) }
+relation Perm([], []) -- s2
+relation Perm(z, [x | y]) -- s3 { Perm(z2, y) Del(x, z, z2) }
+relation Del(x, [x | y], y) -- s4
+relation Del(x, [y | z], [y | z2]) -- s5 { Del(x, z, z2) }
+relation Ord([]) -- s6
+relation Ord([_x]) -- s7
+relation Ord([x, y | z]) -- s8 { LE(x, y) Ord([y | z]) }
+relation LE(1, 2) -- s9
+relation LE(1, 3) -- s10
+relation LE(2, 3) -- s11
+relation LE(x, x) -- s12
+
+print find u limit 1 {
+  Sort([2, 1, 3], u)
+}
+
+print find [x, y] limit 10 {
+  Sort(x, y)
+}
+
+// The difference between performance
+// become clear when we ask for 2000 answers.
+
+// print find [x, y] limit 2000 {
+//   Sort(x, y)
+// }
diff --git a/docs/tests/relation/sequencing-of-procedure-calls.ch.out b/docs/examples/tests/relation/sequencing-of-procedure-calls.ch.out
similarity index 100%
rename from docs/tests/relation/sequencing-of-procedure-calls.ch.out
rename to docs/examples/tests/relation/sequencing-of-procedure-calls.ch.out
diff --git a/docs/tests/term/my-list.ch b/docs/examples/tests/term/my-list.ch
similarity index 82%
rename from docs/tests/term/my-list.ch
rename to docs/examples/tests/term/my-list.ch
index 78a3abaf..8bbd9f21 100644
--- a/docs/tests/term/my-list.ch
+++ b/docs/examples/tests/term/my-list.ch
@@ -1,5 +1,5 @@
-clause List(List::Null())
-clause List(List::Cons(_head, tail)) -- { List(tail) }
+relation List(List::Null())
+relation List(List::Cons(_head, tail)) -- { List(tail) }
 
 print find _ {
   List(List::Null())
diff --git a/docs/tests/term/my-list.ch.out b/docs/examples/tests/term/my-list.ch.out
similarity index 100%
rename from docs/tests/term/my-list.ch.out
rename to docs/examples/tests/term/my-list.ch.out
diff --git a/docs/tests/termination/always.ch b/docs/examples/tests/termination/always.ch
similarity index 95%
rename from docs/tests/termination/always.ch
rename to docs/examples/tests/termination/always.ch
index a0d661d1..10d50ebb 100644
--- a/docs/tests/termination/always.ch
+++ b/docs/examples/tests/termination/always.ch
@@ -1,5 +1,5 @@
-clause Always() -- base
-clause Always() -- loop { Always() }
+relation Always() -- base
+relation Always() -- loop { Always() }
 
 print find _ limit 3 {
   Always()
diff --git a/docs/tests/termination/always.ch.out b/docs/examples/tests/termination/always.ch.out
similarity index 100%
rename from docs/tests/termination/always.ch.out
rename to docs/examples/tests/termination/always.ch.out
diff --git a/docs/tests/termination/append.ch b/docs/examples/tests/termination/append.ch
similarity index 84%
rename from docs/tests/termination/append.ch
rename to docs/examples/tests/termination/append.ch
index 0c2702d1..308cd334 100644
--- a/docs/tests/termination/append.ch
+++ b/docs/examples/tests/termination/append.ch
@@ -1,6 +1,6 @@
-clause Append([], t, t)
+relation Append([], t, t)
 
-clause Append([a | d], t, out)
+relation Append([a | d], t, out)
 ------------------------- {
   Append(d, t, res)
   Equal(out, [a | res])
@@ -19,9 +19,9 @@ print find [x, y] limit 6 {
 // We can avoid this problem if we swap the last two lines of `Append`.
 // "FF" means finite failure.
 
-clause AppendFF([], t, t)
+relation AppendFF([], t, t)
 
-clause AppendFF([a | d], t, out)
+relation AppendFF([a | d], t, out)
 -------------------------------------- {
   Equal(out, [a | res])
   AppendFF(d, t, res)
diff --git a/docs/tests/termination/append.ch.out b/docs/examples/tests/termination/append.ch.out
similarity index 100%
rename from docs/tests/termination/append.ch.out
rename to docs/examples/tests/termination/append.ch.out
diff --git a/docs/examples/tests/termination/never.ch b/docs/examples/tests/termination/never.ch
new file mode 100644
index 00000000..17033e3e
--- /dev/null
+++ b/docs/examples/tests/termination/never.ch
@@ -0,0 +1,23 @@
+relation Never(x)
+--------- {
+  Never(x)
+}
+
+relation OneTwoThreeThenNever(1)
+relation OneTwoThreeThenNever(x) -- { Never(x) }
+relation OneTwoThreeThenNever(2)
+relation OneTwoThreeThenNever(x) -- { Never(x) }
+relation OneTwoThreeThenNever(3)
+relation OneTwoThreeThenNever(x) -- { Never(x) }
+
+// Ok:
+
+print find x limit 3 {
+  OneTwoThreeThenNever(x)
+}
+
+// Loop forever:
+
+// print find x limit 4 {
+//   OneTwoThreeThenNever(x)
+// }
diff --git a/docs/tests/termination/never.ch.out b/docs/examples/tests/termination/never.ch.out
similarity index 100%
rename from docs/tests/termination/never.ch.out
rename to docs/examples/tests/termination/never.ch.out
diff --git a/docs/tests/unification/infix-notation-equal.ch b/docs/examples/tests/unification/infix-notation-equal.ch
similarity index 100%
rename from docs/tests/unification/infix-notation-equal.ch
rename to docs/examples/tests/unification/infix-notation-equal.ch
diff --git a/docs/tests/unification/infix-notation-equal.ch.out b/docs/examples/tests/unification/infix-notation-equal.ch.out
similarity index 100%
rename from docs/tests/unification/infix-notation-equal.ch.out
rename to docs/examples/tests/unification/infix-notation-equal.ch.out
diff --git a/docs/tests/unification/infix-notation-not-equal.ch b/docs/examples/tests/unification/infix-notation-not-equal.ch
similarity index 100%
rename from docs/tests/unification/infix-notation-not-equal.ch
rename to docs/examples/tests/unification/infix-notation-not-equal.ch
diff --git a/docs/tests/unification/infix-notation-not-equal.ch.out b/docs/examples/tests/unification/infix-notation-not-equal.ch.out
similarity index 100%
rename from docs/tests/unification/infix-notation-not-equal.ch.out
rename to docs/examples/tests/unification/infix-notation-not-equal.ch.out
diff --git a/docs/tests/unification/occur-check.ch b/docs/examples/tests/unification/occur-check.ch
similarity index 100%
rename from docs/tests/unification/occur-check.ch
rename to docs/examples/tests/unification/occur-check.ch
diff --git a/docs/tests/unification/occur-check.ch.out b/docs/examples/tests/unification/occur-check.ch.out
similarity index 100%
rename from docs/tests/unification/occur-check.ch.out
rename to docs/examples/tests/unification/occur-check.ch.out
diff --git a/docs/std/list/Append.ch b/docs/std/list/Append.ch
deleted file mode 100644
index 13b3a14b..00000000
--- a/docs/std/list/Append.ch
+++ /dev/null
@@ -1,6 +0,0 @@
-export { Append }
-
-clause Append([], l, l)
-clause Append([a | d], l, [a | r]) -- {
-  Append(d, l, r)
-}
diff --git a/docs/std/nat/Nat.ch b/docs/std/nat/Nat.ch
deleted file mode 100644
index 3f1ebbf4..00000000
--- a/docs/std/nat/Nat.ch
+++ /dev/null
@@ -1,7 +0,0 @@
-export { Nat, Zero, Add1 }
-
-clause Nat(Nat::Zero())
-clause Nat(Nat::Add1(prev)) -- { Nat(prev) }
-
-clause Zero(Nat::Zero())
-clause Add1(prev, Nat::Add1(prev))
diff --git a/docs/std/nat/numbers.ch b/docs/std/nat/numbers.ch
deleted file mode 100644
index 46729ce2..00000000
--- a/docs/std/nat/numbers.ch
+++ /dev/null
@@ -1,14 +0,0 @@
-import { Zero, Add1 } from "Nat.ch"
-
-export clause One(n) -- { Add1(prev, n) Zero(prev) }
-export clause Two(n) -- { Add1(prev, n) One(prev) }
-export clause Three(n) -- { Add1(prev, n) Two(prev) }
-export clause Four(n) -- { Add1(prev, n) Three(prev) }
-export clause Five(n) -- { Add1(prev, n) Four(prev) }
-export clause Six(n) -- { Add1(prev, n) Five(prev) }
-export clause Seven(n) -- { Add1(prev, n) Six(prev) }
-export clause Eight(n) -- { Add1(prev, n) Seven(prev) }
-export clause Nine(n) -- { Add1(prev, n) Eight(prev) }
-export clause Ten(n) -- { Add1(prev, n) Nine(prev) }
-export clause Eleven(n) -- { Add1(prev, n) Ten(prev) }
-export clause Twelve(n) -- { Add1(prev, n) Eleven(prev) }
diff --git a/docs/std/trilean/Trilean.ch b/docs/std/trilean/Trilean.ch
deleted file mode 100644
index 1d3421f9..00000000
--- a/docs/std/trilean/Trilean.ch
+++ /dev/null
@@ -1,62 +0,0 @@
-// Use logic programming to play with many-valued logic.
-
-clause Trilean(0)
-clause Trilean(0.5)
-clause Trilean(1)
-
-// Name of the three values:
-
-clause TrileanFalse(0)
-clause TrileanMiddle(0.5)
-clause TrileanTrue(1)
-
-clause TrileanMin(0, 0, 0)
-clause TrileanMin(0, 0.5, 0)
-clause TrileanMin(0, 1, 0)
-clause TrileanMin(0.5, 0, 0)
-clause TrileanMin(0.5, 0.5, 0.5)
-clause TrileanMin(0.5, 1, 0.5)
-clause TrileanMin(1, 0, 0)
-clause TrileanMin(1, 0.5, 0.5)
-clause TrileanMin(1, 1, 1)
-
-clause TrileanMax(0, 0, 0)
-clause TrileanMax(0, 0.5, 0.5)
-clause TrileanMax(0, 1, 1)
-clause TrileanMax(0.5, 0, 0.5)
-clause TrileanMax(0.5, 0.5, 0.5)
-clause TrileanMax(0.5, 1, 1)
-clause TrileanMax(1, 0, 1)
-clause TrileanMax(1, 0.5, 1)
-clause TrileanMax(1, 1, 1)
-
-clause TrileanPositive(0.5)
-clause TrileanPositive(1)
-
-// Use mutually exclusive cases.
-
-clause TrileanMul(0, y, 0) -- { Trilean(y) }
-clause TrileanMul(x, 0, 0) -- { TrileanPositive(x) }
-clause TrileanMul(x, y, z) -- {
-  TrileanPositive(x)
-  TrileanPositive(y)
-  TrileanMax(x, y, z)
-}
-
-// See how `TrileanMax` is different from `TrileanMul`:
-
-print find [x, y, z] { TrileanMax(x, y, z) }
-print find [x, y, z] { TrileanMul(x, y, z) }
-
-// What returns 0?
-print find [x, y] { TrileanMul(x, y, 0) }
-
-// [question] Can `TrileansMul` be defined by
-// composition of other connectives (not, min, max)?
-// Does this means to use only one clause?
-
-// [question] How to search high-order things
-// like connective in logic programming?
-// We want to search how to construct truth function
-// by composition of given set of connectives.
-// Maybe we must define first order expressions first.
diff --git a/docs/tests/conventions/relation-arity-mismatch.error.ch b/docs/tests/conventions/relation-arity-mismatch.error.ch
deleted file mode 100644
index 1c43f45f..00000000
--- a/docs/tests/conventions/relation-arity-mismatch.error.ch
+++ /dev/null
@@ -1,2 +0,0 @@
-clause F(1)
-clause F(1, 2)
diff --git a/docs/tests/conventions/relation-name-must-starts-with-uppercase.error.ch b/docs/tests/conventions/relation-name-must-starts-with-uppercase.error.ch
deleted file mode 100644
index caf26d2b..00000000
--- a/docs/tests/conventions/relation-name-must-starts-with-uppercase.error.ch
+++ /dev/null
@@ -1 +0,0 @@
-clause border("sussex", "kent")
diff --git a/docs/tests/conventions/relation-name-must-starts-with-uppercase.error.ch.err b/docs/tests/conventions/relation-name-must-starts-with-uppercase.error.ch.err
deleted file mode 100644
index e5b356f2..00000000
--- a/docs/tests/conventions/relation-name-must-starts-with-uppercase.error.ch.err
+++ /dev/null
@@ -1,14 +0,0 @@
-I found syntax error in code:
-
- 1 |clause border("sussex", "kent")
- 2 |
-
-
-Found the identifier "border" in [7, 13], while expecting:
- ["identifier"]:
-     stmt:clause_no_goals_no_name@0 -> "clause"@1 > (name: identifier) (args: args) 
- ["identifier"]:
-     stmt:clause_no_goals@0 -> "clause"@1 > (name: identifier) (args: args) dashline (clause_name: identifier) 
- ["identifier"]:
-     stmt:clause_no_name@0 -> "clause"@1 > (name: identifier) (args: args) dashline "{" (goals: goals) "}" 
- and so on ...
diff --git a/docs/tests/module/example.ch b/docs/tests/module/example.ch
deleted file mode 100644
index bfbd4866..00000000
--- a/docs/tests/module/example.ch
+++ /dev/null
@@ -1,5 +0,0 @@
-export clause Hello("Hello, World!")
-
-export clause Hi("Hi there!")
-
-clause Hiya("Hiya!")
diff --git a/docs/tests/relation/datom.ch b/docs/tests/relation/datom.ch
deleted file mode 100644
index 3a94878e..00000000
--- a/docs/tests/relation/datom.ch
+++ /dev/null
@@ -1,9 +0,0 @@
-clause Datom(1, "name", "A")
-clause Datom(1, "age", 45)
-clause Datom(2, "name", "X")
-clause Datom(2, "age", 2)
-
-print find n {
-  Datom(e, "age", 2)
-  Datom(e, "name", n)
-}
diff --git a/docs/tests/relation/sequencing-of-procedure-calls.ch b/docs/tests/relation/sequencing-of-procedure-calls.ch
deleted file mode 100644
index d9b22840..00000000
--- a/docs/tests/relation/sequencing-of-procedure-calls.ch
+++ /dev/null
@@ -1,35 +0,0 @@
-// Example taken from Robert Kowalski's paper
-// "Predicate logic as a programming language"
-// Chapter "11. SEQUENCING OF PROCEDURE CALLS"
-
-// The point is that doing `Ord` before `Perm`
-// is more efficient.
-
-// clause Sort(x, y) -- s1 { Perm(x, y) Ord(y) }
-clause Sort(x, y) -- s1 { Ord(y) Perm(x, y) }
-clause Perm([], []) -- s2
-clause Perm(z, [x | y]) -- s3 { Perm(z2, y) Del(x, z, z2) }
-clause Del(x, [x | y], y) -- s4
-clause Del(x, [y | z], [y | z2]) -- s5 { Del(x, z, z2) }
-clause Ord([]) -- s6
-clause Ord([_x]) -- s7
-clause Ord([x, y | z]) -- s8 { LE(x, y) Ord([y | z]) }
-clause LE(1, 2) -- s9
-clause LE(1, 3) -- s10
-clause LE(2, 3) -- s11
-clause LE(x, x) -- s12
-
-print find u limit 1 {
-  Sort([2, 1, 3], u)
-}
-
-print find [x, y] limit 10 {
-  Sort(x, y)
-}
-
-// The difference between performance
-// become clear when we ask for 2000 answers.
-
-// print find [x, y] limit 2000 {
-//   Sort(x, y)
-// }
diff --git a/docs/tests/termination/never.ch b/docs/tests/termination/never.ch
deleted file mode 100644
index 5718a4b3..00000000
--- a/docs/tests/termination/never.ch
+++ /dev/null
@@ -1,23 +0,0 @@
-clause Never(x)
---------- {
-  Never(x)
-}
-
-clause OneTwoThreeThenNever(1)
-clause OneTwoThreeThenNever(x) -- { Never(x) }
-clause OneTwoThreeThenNever(2)
-clause OneTwoThreeThenNever(x) -- { Never(x) }
-clause OneTwoThreeThenNever(3)
-clause OneTwoThreeThenNever(x) -- { Never(x) }
-
-// Ok:
-
-print find x limit 3 {
-  OneTwoThreeThenNever(x)
-}
-
-// Loop forever:
-
-// print find x limit 4 {
-//   OneTwoThreeThenNever(x)
-// }
diff --git a/src/lang/globals/aboutBoolean.ts b/src/lang/globals/aboutBoolean.ts
index eab10488..54efa4ec 100644
--- a/src/lang/globals/aboutBoolean.ts
+++ b/src/lang/globals/aboutBoolean.ts
@@ -5,8 +5,8 @@ import type { GlobalStore } from "./GlobalStore.js"
 export function aboutBoolean(globals: GlobalStore): void {
   globals.code(`
 
-clause Boolean(x) -- { Equal(x, false) }
-clause Boolean(x) -- { Equal(x, true) }
+relation Boolean(x) -- { Equal(x, false) }
+relation Boolean(x) -- { Equal(x, true) }
 
 `)
 }
diff --git a/src/lang/globals/aboutNull.ts b/src/lang/globals/aboutNull.ts
index db0a652d..fc587d27 100644
--- a/src/lang/globals/aboutNull.ts
+++ b/src/lang/globals/aboutNull.ts
@@ -3,7 +3,7 @@ import type { GlobalStore } from "./GlobalStore.js"
 export function aboutNull(globals: GlobalStore): void {
   globals.code(`
 
-clause Null(x) -- { Equal(x, null) }
+relation Null(x) -- { Equal(x, null) }
 
 `)
 }
diff --git a/src/lang/syntax/grammars/stmt.ts b/src/lang/syntax/grammars/stmt.ts
index 984e1635..99973be8 100644
--- a/src/lang/syntax/grammars/stmt.ts
+++ b/src/lang/syntax/grammars/stmt.ts
@@ -1,19 +1,19 @@
 export const stmt = {
   $grammar: {
     "stmt:clause_no_goals_no_name": [
-      '"clause"',
+      '"relation"',
       { name: "relation_name" },
       { args: "args" },
     ],
     "stmt:clause_no_goals": [
-      '"clause"',
+      '"relation"',
       { name: "relation_name" },
       { args: "args" },
       "dashline",
       { clause_name: "clause_name" },
     ],
     "stmt:clause_no_name": [
-      '"clause"',
+      '"relation"',
       { name: "relation_name" },
       { args: "args" },
       "dashline",
@@ -22,7 +22,7 @@ export const stmt = {
       '"}"',
     ],
     "stmt:clause": [
-      '"clause"',
+      '"relation"',
       { name: "relation_name" },
       { args: "args" },
       "dashline",
diff --git a/src/test.ts b/src/test.ts
index ec202e16..9176f196 100644
--- a/src/test.ts
+++ b/src/test.ts
@@ -9,8 +9,8 @@ import { stripAnsi } from "./utils/ansi.js"
 const __filename = fileURLToPath(import.meta.url)
 const __dirname = Path.dirname(__filename)
 
-test("snapshot docs/**/*.ch", async () => {
-  const files = await glob(`${__dirname}/../docs/**/*.ch`)
+test("snapshot docs/examples/**/*.ch", async () => {
+  const files = await glob(`${__dirname}/../docs/examples/**/*.ch`)
   for (const file of files) {
     if (file.endsWith(".error.ch")) {
       await snapshotError(new URL(`file:${file}`))