diff --git a/lib/cpsolver-all-1.3.jar b/lib/cpsolver-all-1.3.jar
index c087139..dc59a5d 100644
Binary files a/lib/cpsolver-all-1.3.jar and b/lib/cpsolver-all-1.3.jar differ
diff --git a/src/ctt.properties b/src/ctt.properties
index de0b143..bc445f5 100644
--- a/src/ctt.properties
+++ b/src/ctt.properties
@@ -42,4 +42,7 @@ SimulatedAnnealing.ReheatLengthCoef=7
 Extensions.Classes=org.cpsolver.ifs.extension.ConflictStatistics
 
 #Other
-General.SaveBestUnassigned=0
\ No newline at end of file
+General.SaveBestUnassigned=0
+
+ParallelSolver.SingleSolution=false
+ParallelSolver.SingleSolutionNeighbourCheck=true
\ No newline at end of file
diff --git a/src/exam.properties b/src/exam.properties
index 96aa8bb..4dbb19b 100644
--- a/src/exam.properties
+++ b/src/exam.properties
@@ -35,4 +35,7 @@ General.SaveBestUnassigned=0
 #Extensions
 Exam.AllowDirectConflict=false
 Exam.AllowBinaryViolations=false
-Extensions.Classes=org.cpsolver.ifs.extension.ConflictStatistics
\ No newline at end of file
+Extensions.Classes=org.cpsolver.ifs.extension.ConflictStatistics
+
+ParallelSolver.SingleSolution=false
+ParallelSolver.SingleSolutionNeighbourCheck=true
\ No newline at end of file
diff --git a/src/net/sf/cpsolver/itc/ItcModel.java b/src/net/sf/cpsolver/itc/ItcModel.java
index b58c8e2..45ad107 100644
--- a/src/net/sf/cpsolver/itc/ItcModel.java
+++ b/src/net/sf/cpsolver/itc/ItcModel.java
@@ -54,4 +54,9 @@ public boolean cvsPrint(Assignment<V, T> assignment) {
     public void makeFeasible(Assignment<V, T> assignment) {}
     
     public abstract Assignment<V, T> createAssignment(int index, Assignment<V, T> assignment);
+    
+    @Override
+    public String toString(Assignment<V, T> a) {
+    	return "V:"+a.nrAssignedVariables()+"/"+variables().size()+", P:"+Math.round(getTotalValue(a))+" ("+csvLine(a)+")";
+    }
 }
diff --git a/src/net/sf/cpsolver/itc/ItcTest.java b/src/net/sf/cpsolver/itc/ItcTest.java
index 7130faf..55badbf 100644
--- a/src/net/sf/cpsolver/itc/ItcTest.java
+++ b/src/net/sf/cpsolver/itc/ItcTest.java
@@ -4,6 +4,8 @@
 import java.io.FileWriter;
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.lang.management.ManagementFactory;
+import java.lang.management.OperatingSystemMXBean;
 import java.text.DecimalFormat;
 import java.util.Collection;
 import java.util.List;
@@ -250,24 +252,27 @@ protected Solution createParallelSolution(int index) {
                     solution.addSolutionListener(listener);
                 return solution;
             }
+        	@Override
+            public boolean hasSingleSolution() {
+        		return sConfig.getPropertyBoolean("ParallelSolver.SingleSolution", false);
+        	}
         };
 		Solution solution = new Solution(model, model.createAssignment(0, null));
         solver.setInitalSolution(solution);
+        solution.getModel().createAssignmentContexts(solution.getAssignment(), false);
         
         solver.currentSolution().addSolutionListener(new SolutionListener() {
-            public void solutionUpdated(Solution solution) {}
+            public void solutionUpdated(Solution solution) {
+            	//sLog.info("**CURRENT["+solution.getIteration()+"]** " + solution);
+            }
             public void getInfo(Solution solution, Map info) {}
             public void getInfo(Solution solution, Map info, Collection variables) {}
             public void bestCleared(Solution solution) {}
             public void bestSaved(Solution solution) {
-                ItcModel m = (ItcModel)solution.getModel();
-                Assignment a = solution.getAssignment();
-                sLog.info("**BEST["+solution.getIteration()+"]** V:"+a.nrAssignedVariables()+"/"+m.variables().size()+", P:"+Math.round(m.getTotalValue(a))+" ("+m.csvLine(a)+")");
+                sLog.info("**BEST["+solution.getIteration()+"]** " + solution);
             }
             public void bestRestored(Solution solution) {
-                ItcModel m = (ItcModel)solution.getModel();
-                Assignment a = solution.getAssignment();
-            	sLog.info("##RESTORED["+solution.getIteration()+"]## V:"+a.nrAssignedVariables()+"/"+m.variables().size()+", P:"+Math.round(m.getTotalValue(a))+" ("+m.csvLine(a)+")");
+            	sLog.info("##RESTORED["+solution.getIteration()+"]## " + solution);
             }
         });
         
@@ -287,7 +292,7 @@ public static Solution solve() {
             Solution solution = solver.currentSolution();
             solution.restoreBest();
             ((ItcModel)solution.getModel()).makeFeasible(solution.getAssignment());
-            solution.saveBest();
+            // solution.saveBest();
             
             return output(solver);
         } catch (Exception e) {
@@ -305,7 +310,7 @@ private static Solution output(Solver solver) throws Exception {
             sLog.error("No best solution found.");
             return null;
         }
-        solution.restoreBest();
+        // solution.restoreBest();
         
         sLog.info("Best solution:"+ToolBox.dict2string(solution.getExtendedInfo(),1));
         
@@ -325,6 +330,11 @@ private static Solution output(Solver solver) throws Exception {
             ItcModel m = (ItcModel)solution.getModel();
             Assignment a = solution.getAssignment();
             DecimalFormat df = new DecimalFormat("0.00");
+            double cpu = 0.0;
+            OperatingSystemMXBean bean = ManagementFactory.getOperatingSystemMXBean();
+            if (bean instanceof com.sun.management.OperatingSystemMXBean) {
+            	cpu = ((com.sun.management.OperatingSystemMXBean)bean).getProcessCpuTime() / 1e9;
+            }
             w.println(
                     sSeed+","+
                     sTimeOut+","+
@@ -332,7 +342,10 @@ private static Solution output(Solver solver) throws Exception {
                     solution.getBestIteration()+","+
                     Math.round(m.getTotalValue(solution.getAssignment()) + 5000 * a.nrUnassignedVariables(m))+","+
                     model.csvLine(a) + "," +
-                    model.getProperties().getPropertyInt("Parallel.NrSolvers", 4));
+                    model.getProperties().getPropertyInt("Parallel.NrSolvers", 4) +
+                    (solver.hasSingleSolution() ? "s": "p") +
+                    (solver.hasSingleSolution() && model.getProperties().getPropertyBoolean("ParallelSolver.SingleSolutionQueue", true) ? "q" : "") + "," +
+                    df.format(solution.getIteration() / solution.getTime()) + "," + df.format(cpu));
             w.flush(); w.close();
         }
         
@@ -353,7 +366,7 @@ public void run() {
                 Solution solution = iSolver.currentSolution();
                 solution.restoreBest();
                 ((ItcModel)solution.getModel()).makeFeasible(solution.getAssignment());
-                solution.saveBest();
+                // solution.saveBest();
                 
                 output(iSolver);
             } catch (Exception e) {
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttAssignment.java b/src/net/sf/cpsolver/itc/ctt/model/CttAssignment.java
index 9661ca6..729320a 100644
--- a/src/net/sf/cpsolver/itc/ctt/model/CttAssignment.java
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttAssignment.java
@@ -7,6 +7,7 @@
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.AssignmentAbstract;
+import org.cpsolver.ifs.assignment.context.AssignmentContextHolder;
 import org.cpsolver.ifs.assignment.context.DefaultParallelAssignmentContextHolder;
 import org.cpsolver.ifs.model.Model;
 
@@ -34,17 +35,28 @@
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
 public class CttAssignment extends AssignmentAbstract<CttLecture, CttPlacement> {
-	private CttModel iModel;
-	private int iIndex;
-	private int iNrAssigned = 0;
+	protected CttModel iModel;
+	protected int iIndex;
+	protected int iNrAssigned = 0;
+	protected CttPlacement[] iAssignment = null;
+	protected CttAssignment iParent = null;
 	
 	public CttAssignment(CttModel model, int index, Assignment<CttLecture, CttPlacement> assignment) {
 		super(new DefaultParallelAssignmentContextHolder<CttLecture, CttPlacement>(index));
 		iIndex = index;
 		iModel = model;
-		if (assignment != null)
-            for (CttPlacement value: assignment.assignedValues())
-                setValueInternal(0, value.variable(), value);
+		iParent = (CttAssignment) assignment;
+		if (iParent == null) {
+			iAssignment = new CttPlacement[model.variables().size()];
+			iNrAssigned = 0;
+		} else {
+			iAssignment = Arrays.copyOf(((CttAssignment)iParent).toArray(), model.variables().size());
+			iNrAssigned = iParent.nrAssignedVariables();
+		}
+	}
+	
+	protected CttAssignment(AssignmentContextHolder<CttLecture, CttPlacement> contextHolder) {
+		super(contextHolder);
 	}
 	
 	@Override
@@ -97,35 +109,16 @@ public Collection<CttLecture> assignedVariables() {
 		return assigned;
 	}
 
-    protected CttPlacement[] getAssignments(CttLecture variable) {
-        synchronized (variable) {
-            CttPlacement[] assignments = (CttPlacement[])variable.getExtra();
-            if (assignments == null) {
-                assignments = (CttPlacement[])new CttPlacement[Math.max(10, 1 + iIndex)];
-                variable.setExtra(assignments);
-            } else if (assignments.length <= iIndex) {
-                assignments = Arrays.copyOf(assignments, 10 + iIndex);
-                variable.setExtra(assignments);
-            }
-            return assignments;
-        }
-    }
-    
 	@Override
-    @SuppressWarnings("deprecation")
     protected CttPlacement getValueInternal(CttLecture variable) {
-    	if (iIndex == 1)
-    		return variable.getAssignment();
-        return getAssignments(variable)[iIndex];
+        // return (CttPlacement) variable.getAssignments()[iIndex];
+		return iAssignment[variable.getIndex()];
     }
     
 	@Override
-    @SuppressWarnings("deprecation")
     protected void setValueInternal(long iteration, CttLecture variable, CttPlacement value) {
-    	if (iIndex == 1)
-    		variable.setAssignment(value);
-    	else
-    		getAssignments(variable)[iIndex] = value;
+    	//variable.getAssignments()[iIndex] = value;
+    	iAssignment[variable.getIndex()] = value;
         if (value == null)
         	iNrAssigned --;
         else
@@ -141,4 +134,12 @@ public int getIndex() {
     public int nrAssignedVariables() {
         return iNrAssigned;
     }
+    
+    public CttPlacement[] toArray() {
+    	return iAssignment;
+    }
+
+	public Assignment<CttLecture, CttPlacement> getParentAssignment() {
+		return iParent;
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttCurricula.java b/src/net/sf/cpsolver/itc/ctt/model/CttCurricula.java
index 891f69f..9ac3d32 100644
--- a/src/net/sf/cpsolver/itc/ctt/model/CttCurricula.java
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttCurricula.java
@@ -1,12 +1,14 @@
 package net.sf.cpsolver.itc.ctt.model;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.assignment.context.ConstraintWithContext;
 import org.cpsolver.ifs.model.ConstraintListener;
 
@@ -148,7 +150,7 @@ public int getCompactPenalty(Assignment<CttLecture, CttPlacement> assignment, Ct
      * same curricula are placed at the same time.
      *
      */
-    public class CurriculaConstraint extends ConstraintWithContext<CttLecture, CttPlacement, CttCurricula.Table> {
+    public class CurriculaConstraint extends ConstraintWithContext<CttLecture, CttPlacement, CttCurricula.Table> implements CanInheritContext<CttLecture, CttPlacement, CttCurricula.Table> {
         
         /** Constructor */
         public CurriculaConstraint() {
@@ -212,9 +214,14 @@ public int hashCode() {
 		public Table createAssignmentContext(Assignment<CttLecture, CttPlacement> assignment) {
 			return new Table(assignment);
 		}
+
+		@Override
+		public Table inheritAssignmentContext(Assignment<CttLecture, CttPlacement> assignment, Table parentContext) {
+			return new Table(assignment, parentContext);
+		}
     }
     
-    private class Table implements AssignmentConstraintContext<CttLecture, CttPlacement> {
+    public class Table implements AssignmentConstraintContext<CttLecture, CttPlacement> {
         public CttPlacement[] iPlacement;
         
         public Table(Assignment<CttLecture, CttPlacement> assignment) {
@@ -226,6 +233,10 @@ public Table(Assignment<CttLecture, CttPlacement> assignment) {
 				if (p != null) assigned(assignment, p);
 			}
 		}
+        
+        public Table(Assignment<CttLecture, CttPlacement> assignment, Table parent) {
+        	iPlacement = Arrays.copyOf(parent.iPlacement, parent.iPlacement.length);
+        }
 
 		@Override
 		public void assigned(Assignment<CttLecture, CttPlacement> assignment, CttPlacement p) {
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttInheritedAssignment.java b/src/net/sf/cpsolver/itc/ctt/model/CttInheritedAssignment.java
new file mode 100644
index 0000000..03cec4c
--- /dev/null
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttInheritedAssignment.java
@@ -0,0 +1,56 @@
+package net.sf.cpsolver.itc.ctt.model;
+
+import java.util.Arrays;
+import java.util.concurrent.locks.Lock;
+
+import org.cpsolver.ifs.assignment.InheritedAssignment;
+import org.cpsolver.ifs.assignment.context.InheritedAssignmentContextHolder;
+import org.cpsolver.ifs.solution.Solution;
+
+/**
+ * Curriculum based Course Timetabling (CTT) inherited assignment model.
+ * 
+ * @version
+ * ITC2007 1.0<br>
+ * Copyright (C) 2014 Tomas Muller<br>
+ * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
+ * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
+ * <br>
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ * <br><br>
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * <br><br>
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not see
+ * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
+ */
+public class CttInheritedAssignment extends CttAssignment implements InheritedAssignment<CttLecture, CttPlacement> {
+	private long iVersion = -1;
+
+	public CttInheritedAssignment(Solution<CttLecture, CttPlacement> solution, int index) {
+		super(new InheritedAssignmentContextHolder<CttLecture, CttPlacement>(index, solution.getIteration()));
+		iIndex = index;
+		iVersion = solution.getIteration();
+		iModel = (CttModel) solution.getModel();
+		iParent = (CttAssignment) solution.getAssignment();
+		Lock lock = solution.getLock().readLock();
+		lock.lock();
+		try {
+			iNrAssigned = iParent.nrAssignedVariables();
+			iAssignment = Arrays.copyOf(((CttAssignment)iParent).toArray(), iModel.variables().size());
+		} finally {
+			lock.unlock();
+		}
+	}
+	
+	@Override
+	public long getVersion() {
+		return iVersion;
+	}
+}
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttLecture.java b/src/net/sf/cpsolver/itc/ctt/model/CttLecture.java
index cf95b81..81fee96 100644
--- a/src/net/sf/cpsolver/itc/ctt/model/CttLecture.java
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttLecture.java
@@ -4,9 +4,10 @@
 import java.util.List;
 
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.model.LazySwap;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.model.Variable;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazySwap;
+
 import net.sf.cpsolver.itc.heuristics.neighbour.ItcSwap.Swapable;
 
 /**
@@ -37,6 +38,7 @@
 public class CttLecture extends Variable<CttLecture, CttPlacement> implements Swapable<CttLecture, CttPlacement> {
     private int iIdx;
     private CttCourse iCourse = null;
+    private int iHashCode;
     
     /** Constructor
      * @param course course to which this lecture belongs
@@ -54,6 +56,7 @@ public CttLecture(CttCourse course, int idx) {
             curricula.getConstraint().addVariable(this);
         setValues(computeValues());
         getModel().addVariable(this);
+        iHashCode = toString().hashCode();
     }
     
     /** Return course to which this lecture belong */
@@ -102,7 +105,7 @@ public boolean equals(Object o) {
     
     /** Hash code */
     public int hashCode() {
-        return toString().hashCode();
+        return iHashCode;
     }
     
     /** Compare two lectures, return the harder one. That is the one with more curriculas, or smaller domain/constraint ratio. */
@@ -142,7 +145,7 @@ public Neighbour<CttLecture, CttPlacement> findSwap(Assignment<CttLecture, CttPl
         }
         CttPlacement np1 = new CttPlacement(this, p2.getRoom(), p2.getDay(), p2.getSlot());
         CttPlacement np2 = new CttPlacement(lecture, p1.getRoom(), p1.getDay(), p1.getSlot());
-        return new ItcLazySwap<CttLecture, CttPlacement>(assignment, np1, np2);
+        return new LazySwap<CttLecture, CttPlacement>(np1, np2);
         /*
         double value = 0;
         //value += np1.extraPenalty() + np2.extraPenalty() - p1.extraPenalty() - p2.extraPenalty();
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttModel.java b/src/net/sf/cpsolver/itc/ctt/model/CttModel.java
index 9ff6f7b..2b6f4f6 100644
--- a/src/net/sf/cpsolver/itc/ctt/model/CttModel.java
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttModel.java
@@ -11,9 +11,12 @@
 import java.util.StringTokenizer;
 
 import org.apache.log4j.Logger;
-
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.InheritedAssignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
+import org.cpsolver.ifs.solution.Solution;
+
 import net.sf.cpsolver.itc.ItcModel;
 
 /**
@@ -39,7 +42,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class CttModel extends ItcModel<CttLecture, CttPlacement> {
+public class CttModel extends ItcModel<CttLecture, CttPlacement> implements CanInheritContext<CttLecture, CttPlacement, AssignmentConstraintContext<CttLecture, CttPlacement>> {
     private static Logger sLog = Logger.getLogger(CttModel.class); 
     private String iName = null;
     private int iNrDays = 0;
@@ -345,6 +348,12 @@ public AssignmentConstraintContext<CttLecture, CttPlacement> createAssignmentCon
 		return new Penalties(assignment);
 	}
 	
+	@Override
+	public AssignmentConstraintContext<CttLecture, CttPlacement> inheritAssignmentContext(Assignment<CttLecture, CttPlacement> assignment,
+			AssignmentConstraintContext<CttLecture, CttPlacement> parentContext) {
+		return new Penalties(assignment, (Penalties)parentContext);
+	}
+	
     /**
      * Update penalty counters when a variable is unassigned 
      */
@@ -361,7 +370,6 @@ public void beforeAssigned(Assignment<CttLecture, CttPlacement> assignment, long
         getPenalties(assignment).beforeAssigned(assignment, placement);
     }
 
-    
     private class Penalties implements AssignmentConstraintContext<CttLecture, CttPlacement> {
         private int iCompactPenalty = 0;
         private int iRoomPenalty = 0;
@@ -375,6 +383,13 @@ public Penalties(Assignment<CttLecture, CttPlacement> assignment) {
 			iRoomCapPenalty = CttModel.this.getRoomCapPenalty(assignment, true);
 		}
 		
+		public Penalties(Assignment<CttLecture, CttPlacement> assignment, Penalties parent) {
+			iCompactPenalty = parent.getCompactPenalty();
+			iRoomPenalty = parent.getRoomPenalty();
+			iMinDaysPenalty = parent.getMinDaysPenalty();
+			iRoomCapPenalty = parent.getRoomCapPenalty();
+		}
+		
 		@Override
 		public void assigned(Assignment<CttLecture, CttPlacement> assignment, CttPlacement placement) {}
 		
@@ -408,9 +423,14 @@ public void afterUnassigned(Assignment<CttLecture, CttPlacement> assignment, Ctt
 		public int getRoomCapPenalty() { return iRoomCapPenalty; }
     }
 
-
 	@Override
 	public Assignment<CttLecture, CttPlacement> createAssignment(int index, Assignment<CttLecture, CttPlacement> assignment) {
 		return new CttAssignment(this, index, assignment);
 	}
+
+	@Override
+    public InheritedAssignment<CttLecture, CttPlacement> createInheritedAssignment(Solution<CttLecture, CttPlacement> solution, int index) {
+        return new CttInheritedAssignment(solution, index);
+    }
+
 }
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttRoom.java b/src/net/sf/cpsolver/itc/ctt/model/CttRoom.java
index 4387220..56e8e79 100644
--- a/src/net/sf/cpsolver/itc/ctt/model/CttRoom.java
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttRoom.java
@@ -1,10 +1,12 @@
 package net.sf.cpsolver.itc.ctt.model;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.assignment.context.ConstraintWithContext;
 import org.cpsolver.ifs.model.ConstraintListener;
 
@@ -91,7 +93,7 @@ public RoomConstraint getConstraint() {
     /** Room constraint. This hard constraint ensures that no two lectures
      * are placed into this room at the same time. 
      */ 
-    public class RoomConstraint extends ConstraintWithContext<CttLecture, CttPlacement, CttRoom.Table> {
+    public class RoomConstraint extends ConstraintWithContext<CttLecture, CttPlacement, CttRoom.Table> implements CanInheritContext<CttLecture, CttPlacement, CttRoom.Table> {
         
         /** Constructor */
         public RoomConstraint() {
@@ -173,6 +175,11 @@ public CttPlacement getPlacement(Assignment<CttLecture, CttPlacement> assignment
 		public Table createAssignmentContext(Assignment<CttLecture, CttPlacement> assignment) {
 			return new Table(assignment);
 		}
+
+		@Override
+		public Table inheritAssignmentContext(Assignment<CttLecture, CttPlacement> assignment, Table parentContext) {
+			return new Table(assignment, parentContext);
+		}
     }
     
     private class Table implements AssignmentConstraintContext<CttLecture, CttPlacement> {
@@ -186,6 +193,10 @@ public Table(Assignment<CttLecture, CttPlacement> assignment) {
 				if (p.getRoom().equals(CttRoom.this))
 					assigned(assignment, p);
 		}
+        
+        public Table(Assignment<CttLecture, CttPlacement> assignment, Table parent) {
+        	iPlacement = Arrays.copyOf(parent.iPlacement, parent.iPlacement.length);
+        }
 
 		@Override
 		public void assigned(Assignment<CttLecture, CttPlacement> assignment, CttPlacement p) {
diff --git a/src/net/sf/cpsolver/itc/ctt/model/CttTeacher.java b/src/net/sf/cpsolver/itc/ctt/model/CttTeacher.java
index 88af8cc..38c72d9 100644
--- a/src/net/sf/cpsolver/itc/ctt/model/CttTeacher.java
+++ b/src/net/sf/cpsolver/itc/ctt/model/CttTeacher.java
@@ -1,10 +1,12 @@
 package net.sf.cpsolver.itc.ctt.model;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.assignment.context.ConstraintWithContext;
 import org.cpsolver.ifs.model.ConstraintListener;
 
@@ -85,7 +87,7 @@ public TeacherConstraint getConstraint() {
      * lectures that are taught by the same teacher are not placed
      * at the same day and time.
      */
-    public class TeacherConstraint extends ConstraintWithContext<CttLecture, CttPlacement, CttTeacher.Table> {
+    public class TeacherConstraint extends ConstraintWithContext<CttLecture, CttPlacement, CttTeacher.Table> implements CanInheritContext<CttLecture, CttPlacement, CttTeacher.Table> {
 
     	/** Constructor */
         public TeacherConstraint() {
@@ -164,8 +166,13 @@ public int hashCode() {
 		public Table createAssignmentContext(Assignment<CttLecture, CttPlacement> assignment) {
 			return new Table(assignment);
 		}
-    }
 
+		@Override
+		public Table inheritAssignmentContext(Assignment<CttLecture, CttPlacement> assignment, Table parentContext) {
+			return new Table(assignment, parentContext);
+		}
+    }
+    
     private class Table implements AssignmentConstraintContext<CttLecture, CttPlacement> {
         private CttPlacement[] iPlacement;
         
@@ -178,6 +185,10 @@ public Table(Assignment<CttLecture, CttPlacement> assignment) {
 				if (p != null) assigned(assignment, p);
 			}
 		}
+        
+        public Table(Assignment<CttLecture, CttPlacement> assignment, Table parent) {
+        	iPlacement = Arrays.copyOf(parent.iPlacement, parent.iPlacement.length);
+        }
 
 		@Override
 		public void assigned(Assignment<CttLecture, CttPlacement> assignment, CttPlacement p) {
diff --git a/src/net/sf/cpsolver/itc/ctt/neighbours/CttCurriculumCompactnessMove.java b/src/net/sf/cpsolver/itc/ctt/neighbours/CttCurriculumCompactnessMove.java
index 6818dd8..42fac9b 100644
--- a/src/net/sf/cpsolver/itc/ctt/neighbours/CttCurriculumCompactnessMove.java
+++ b/src/net/sf/cpsolver/itc/ctt/neighbours/CttCurriculumCompactnessMove.java
@@ -63,13 +63,14 @@ public Neighbour<CttLecture, CttPlacement> selectNeighbour(Solution<CttLecture,
         int cx = ToolBox.random(model.getCurriculas().size());
         for (int c=0;c<model.getCurriculas().size();c++) {
             CttCurricula curricula = model.getCurriculas().get((c+cx)%model.getCurriculas().size());
+            CttCurricula.Table table = curricula.getConstraint().getContext(assignment);
             List<CttPlacement> adepts = new ArrayList<CttPlacement>();
             for (int d=0;d<model.getNrDays();d++) {
                 for (int s=0;s<model.getNrSlotsPerDay();s++) {
-                    CttPlacement p = curricula.getConstraint().getPlacement(assignment, d, s);
+                    CttPlacement p = table.getPlacement(d, s);
                     if (p==null) continue;
-                    CttPlacement prev = (s==0?null:curricula.getConstraint().getPlacement(assignment, d, s-1));
-                    CttPlacement next = (s+1==model.getNrSlotsPerDay()?null:curricula.getConstraint().getPlacement(assignment, d, s+1));
+                    CttPlacement prev = (s==0?null:table.getPlacement(d, s-1));
+                    CttPlacement next = (s+1==model.getNrSlotsPerDay()?null:table.getPlacement(d, s+1));
                     if (next==null && prev==null) {
                         adepts.add(p);
                     }
diff --git a/src/net/sf/cpsolver/itc/ctt/neighbours/CttSwapMove.java b/src/net/sf/cpsolver/itc/ctt/neighbours/CttSwapMove.java
index ca8c508..973abcb 100644
--- a/src/net/sf/cpsolver/itc/ctt/neighbours/CttSwapMove.java
+++ b/src/net/sf/cpsolver/itc/ctt/neighbours/CttSwapMove.java
@@ -2,17 +2,18 @@
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.heuristics.NeighbourSelection;
+import org.cpsolver.ifs.model.LazySwap;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.solution.Solution;
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
 import org.cpsolver.ifs.util.ToolBox;
+
 import net.sf.cpsolver.itc.ctt.model.CttCurricula;
 import net.sf.cpsolver.itc.ctt.model.CttLecture;
 import net.sf.cpsolver.itc.ctt.model.CttModel;
 import net.sf.cpsolver.itc.ctt.model.CttPlacement;
 import net.sf.cpsolver.itc.ctt.model.CttRoom;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazySwap;
 import net.sf.cpsolver.itc.heuristics.neighbour.ItcSimpleNeighbour;
 import net.sf.cpsolver.itc.heuristics.neighbour.ItcSwap;
 import net.sf.cpsolver.itc.heuristics.search.ItcHillClimber.HillClimberSelection;
@@ -101,7 +102,7 @@ public Neighbour<CttLecture, CttPlacement> selectNeighbour(Solution<CttLecture,
                             CttPlacement conf = curricula.getConstraint().getPlacement(assignment, placement.getDay(), placement.getSlot());
                             if (conf!=null && !conf.variable().equals(lecture)) continue room;
                         }
-                        return new ItcLazySwap<CttLecture, CttPlacement>(assignment,
+                        return new LazySwap<CttLecture, CttPlacement>(
                                 new CttPlacement(lecture, room, day, slot),
                                 new CttPlacement(confLect, placement.getRoom(), placement.getDay(), placement.getSlot()));
                     }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExAssignment.java b/src/net/sf/cpsolver/itc/exam/model/ExAssignment.java
index d6c2db7..fb562d6 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExAssignment.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExAssignment.java
@@ -7,6 +7,7 @@
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.AssignmentAbstract;
+import org.cpsolver.ifs.assignment.context.AssignmentContextHolder;
 import org.cpsolver.ifs.assignment.context.DefaultParallelAssignmentContextHolder;
 import org.cpsolver.ifs.model.BinaryConstraint;
 import org.cpsolver.ifs.model.Model;
@@ -35,17 +36,28 @@
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
 public class ExAssignment extends AssignmentAbstract<ExExam, ExPlacement> {
-	private ExModel iModel;
-	private int iIndex;
-	private int iNrAssigned = 0;
+	protected int iIndex;
+	protected int iNrAssigned = 0;
+	protected ExModel iModel;
+	protected ExPlacement[] iAssignment = null;
+	protected ExAssignment iParent = null;
 	
 	public ExAssignment(ExModel model, int index, Assignment<ExExam, ExPlacement> assignment) {
 		super(new DefaultParallelAssignmentContextHolder<ExExam, ExPlacement>(index));
 		iIndex = index;
 		iModel = model;
-		if (assignment != null)
-            for (ExPlacement value: assignment.assignedValues())
-                setValueInternal(0, value.variable(), value);
+		iParent = (ExAssignment) assignment;
+		if (iParent == null) {
+			iAssignment = new ExPlacement[model.variables().size()];
+			iNrAssigned = 0;
+		} else {
+			iAssignment = Arrays.copyOf(((ExAssignment)iParent).toArray(), model.variables().size());
+			iNrAssigned = iParent.nrAssignedVariables();
+		}
+	}
+	
+	protected ExAssignment(AssignmentContextHolder<ExExam, ExPlacement> contextHolder) {
+		super(contextHolder);
 	}
 	
 	@Override
@@ -119,20 +131,24 @@ protected ExPlacement[] getAssignments(ExExam variable) {
     }
     
 	@Override
-    @SuppressWarnings("deprecation")
     protected ExPlacement getValueInternal(ExExam variable) {
+		return iAssignment[variable.getIndex()];
+		/*
     	if (iIndex == 1)
     		return variable.getAssignment();
         return getAssignments(variable)[iIndex];
+        */
     }
     
 	@Override
-    @SuppressWarnings("deprecation")
     protected void setValueInternal(long iteration, ExExam variable, ExPlacement value) {
+		iAssignment[variable.getIndex()] = value;
+		/*
     	if (iIndex == 1)
     		variable.setAssignment(value);
     	else
     		getAssignments(variable)[iIndex] = value;
+    	*/
         if (value == null)
         	iNrAssigned --;
         else
@@ -148,4 +164,12 @@ public int getIndex() {
     public int nrAssignedVariables() {
         return iNrAssigned;
     }
+    
+    public ExPlacement[] toArray() {
+    	return iAssignment;
+    }
+
+	public Assignment<ExExam, ExPlacement> getParentAssignment() {
+		return iParent;
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExExam.java b/src/net/sf/cpsolver/itc/exam/model/ExExam.java
index 716baea..2a8b086 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExExam.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExExam.java
@@ -8,14 +8,14 @@
 import java.util.Set;
 
 import org.apache.log4j.Logger;
-
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.model.BinaryConstraint;
 import org.cpsolver.ifs.model.Constraint;
+import org.cpsolver.ifs.model.LazySwap;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.model.Variable;
 import org.cpsolver.ifs.util.ToolBox;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazySwap;
+
 import net.sf.cpsolver.itc.heuristics.neighbour.ItcSwap.Swapable;
 
 /**
@@ -225,7 +225,7 @@ public Neighbour<ExExam, ExPlacement> findSwap(Assignment<ExExam, ExPlacement> a
                     if (constraint.inConflict(assignment, np2)) return null;
                 }
             }
-            return new ItcLazySwap<ExExam, ExPlacement>(assignment, np1, np2); 
+            return new LazySwap<ExExam, ExPlacement>(np1, np2); 
         }
         ExRoom r1 = p1.getRoom();
         ExRoom r2 = p2.getRoom();
@@ -235,10 +235,10 @@ public Neighbour<ExExam, ExPlacement> findSwap(Assignment<ExExam, ExPlacement> a
         if (ex2.isRoomExclusive() && r1.getExams(assignment, p1.getPeriod()).size()>1) return null;
         if (!model.areDirectConflictsAllowed() && p1.getPeriodIndex()!=p2.getPeriodIndex()) {
             for (ExStudent s: ex1.getStudents()) {
-                if (s.hasExam(assignment, p2.getPeriod(),ex2)) return null;
+                if (s.getContext(assignment).hasExam(p2.getPeriodIndex(), ex2)) return null;
             }
             for (ExStudent s: ex2.getStudents()) {
-                if (s.hasExam(assignment, p1.getPeriod(),ex1)) return null;
+                if (s.getContext(assignment).hasExam(p1.getPeriodIndex(), ex1)) return null;
             }
         }
         ExPlacement np1 = new ExPlacement(ex1, p2.getPeriod(), p2.getRoom());
@@ -253,7 +253,7 @@ public Neighbour<ExExam, ExPlacement> findSwap(Assignment<ExExam, ExPlacement> a
                 if (constraint.inConflict(assignment, np2)) return null;
             }
         }
-        return new ItcLazySwap<ExExam, ExPlacement>(assignment, np1, np2); 
+        return new LazySwap<ExExam, ExPlacement>(np1, np2); 
     }
     
     /** Compare two exams for equality */
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExInheritedAssignment.java b/src/net/sf/cpsolver/itc/exam/model/ExInheritedAssignment.java
new file mode 100644
index 0000000..f0a3612
--- /dev/null
+++ b/src/net/sf/cpsolver/itc/exam/model/ExInheritedAssignment.java
@@ -0,0 +1,57 @@
+package net.sf.cpsolver.itc.exam.model;
+
+import java.util.Arrays;
+import java.util.concurrent.locks.Lock;
+
+import org.cpsolver.ifs.assignment.InheritedAssignment;
+import org.cpsolver.ifs.assignment.context.InheritedAssignmentContextHolder;
+import org.cpsolver.ifs.solution.Solution;
+
+/**
+ * Examination Timetabling (exam) inherited assignment model.
+ * 
+ * @version
+ * ITC2007 1.0<br>
+ * Copyright (C) 2014 Tomas Muller<br>
+ * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
+ * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
+ * <br>
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ * <br><br>
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * <br><br>
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not see
+ * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
+ */
+public class ExInheritedAssignment extends ExAssignment implements InheritedAssignment<ExExam, ExPlacement> {
+	private long iVersion = -1;
+
+	public ExInheritedAssignment(Solution<ExExam, ExPlacement> solution, int index) {
+		super(new InheritedAssignmentContextHolder<ExExam, ExPlacement>(index, solution.getIteration()));
+		iIndex = index;
+		iVersion = solution.getIteration();
+		iModel = (ExModel) solution.getModel();
+		iParent = (ExAssignment) solution.getAssignment();
+		Lock lock = solution.getLock().readLock();
+		lock.lock();
+		try {
+			iNrAssigned = iParent.nrAssignedVariables();
+			iAssignment = Arrays.copyOf(((ExAssignment)iParent).toArray(), iModel.variables().size());
+		} finally {
+			lock.unlock();
+		}
+	}
+	
+	@Override
+	public long getVersion() {
+		return iVersion;
+	}
+
+}
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExModel.java b/src/net/sf/cpsolver/itc/exam/model/ExModel.java
index 23cfb06..03edce5 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExModel.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExModel.java
@@ -18,11 +18,14 @@
 import java.util.TreeSet;
 
 import org.apache.log4j.Logger;
-
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.InheritedAssignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.model.BinaryConstraint;
 import org.cpsolver.ifs.model.Constraint;
+import org.cpsolver.ifs.solution.Solution;
+
 import net.sf.cpsolver.itc.ItcModel;
 
 /**
@@ -48,7 +51,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class ExModel extends ItcModel<ExExam, ExPlacement> {
+public class ExModel extends ItcModel<ExExam, ExPlacement> implements CanInheritContext<ExExam, ExPlacement, AssignmentConstraintContext<ExExam, ExPlacement>> {
     private static Logger sLog = Logger.getLogger(ExModel.class);
     private List<ExPeriod> iPeriods = new ArrayList<ExPeriod>();
     private List<ExRoom> iRooms = new ArrayList<ExRoom>();
@@ -666,7 +669,7 @@ public int compare(ExExam e1, ExExam e2) {
                 int twoInRowThisExam = 0, twoInDayThisExam = 0, widerSpreadThisExam = 0;
                 for (ExStudent s: exam.getStudents()) {
                     for (ExPeriod p=firstPeriod(); p!=null; p=p.next()) {
-                        if (!s.hasExam(assignment, p)) continue;
+                        if (!s.getContext(assignment).hasExam(p.getIndex())) continue;
                         if (p.getIndex()<=placement.getPeriod().getIndex()) continue;
                         int dist = Math.abs(p.getIndex()-placement.getPeriodIndex());
                         if (p.getDay()==placement.getPeriod().getDay()) {
@@ -769,6 +772,18 @@ public Context(Assignment<ExExam, ExPlacement> assignment) {
     		for (ExPlacement value: assignment.assignedValues())
     			assigned(assignment, value);
     	}
+    	
+    	public Context(Assignment<ExExam, ExPlacement> assignment, Context parent) {
+    		iFronLoadPenalty = parent.iFronLoadPenalty;
+    		iPeriodPenalty = parent.iPeriodPenalty;
+    		iRoomPenalty = parent.iRoomPenalty;
+    		iTwoInARowPenalty = parent.iTwoInARowPenalty;
+    		iTwoInADayPenalty = parent.iTwoInADayPenalty;
+    		iWiderSpreadPenalty = parent.iWiderSpreadPenalty;
+    		iMixedDurationsPenalty = parent.iMixedDurationsPenalty;
+    		iBinaryViolations = parent.iBinaryViolations;
+    		iNrDirectConflicts = parent.iNrDirectConflicts;
+    	}
 
 		@Override
 		public void assigned(Assignment<ExExam, ExPlacement> assignment, ExPlacement placement) {
@@ -820,4 +835,21 @@ public Context getPenalties(Assignment<ExExam, ExPlacement> assignment) {
 	public Assignment<ExExam, ExPlacement> createAssignment(int index, Assignment<ExExam, ExPlacement> assignment) {
 		return new ExAssignment(this, index, assignment);
 	}
+	
+	@Override
+    public InheritedAssignment<ExExam, ExPlacement> createInheritedAssignment(Solution<ExExam, ExPlacement> solution, int index) {
+        return new ExInheritedAssignment(solution, index);
+    }
+
+	@Override
+	public AssignmentConstraintContext<ExExam, ExPlacement> inheritAssignmentContext(Assignment<ExExam, ExPlacement> assignment,
+			AssignmentConstraintContext<ExExam, ExPlacement> parentContext) {
+		return new Context(assignment, (Context)parentContext);
+	}
+	
+	@Override
+	public boolean inConflict(Assignment<ExExam, ExPlacement> assignment, ExPlacement value) {
+		if (value.getRoom().inConflict(assignment, value)) return true;
+		return super.inConflict(assignment, value);
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExPlacement.java b/src/net/sf/cpsolver/itc/exam/model/ExPlacement.java
index 9237153..ff6a920 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExPlacement.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExPlacement.java
@@ -90,9 +90,10 @@ public int twoInARowPenalty(Assignment<ExExam, ExPlacement> assignment) {
         if (!prev && !next) return 0;
         int penalty = 0;
         for (ExStudent student: variable().getStudents()) {
-            if (m.areDirectConflictsAllowed() && student.nrExams(assignment, getPeriod(), exam)>0) continue;
-            if (next && student.hasExam(assignment, nextPeriod,exam)) penalty++;
-            if (prev && student.hasExam(assignment, prevPeriod,exam)) penalty++;
+        	ExStudent.Context cx = student.getContext(assignment);
+            if (m.areDirectConflictsAllowed() && cx.nrExams(getPeriod().getIndex(), exam)>0) continue;
+            if (next && cx.hasExam(nextPeriod.getIndex(), exam)) penalty++;
+            if (prev && cx.hasExam(prevPeriod.getIndex(), exam)) penalty++;
         }
         return penalty;
     }
@@ -103,8 +104,9 @@ public int nrDirectConflicts(Assignment<ExExam, ExPlacement> assignment) {
         ExModel m = (ExModel)exam.getModel();
         if (!m.areDirectConflictsAllowed()) return 0;
         int conflicts = 0;
-        for (ExStudent student: variable().getStudents())
-            if (student.nrExams(assignment, getPeriod(), exam)>0) conflicts++;
+        for (ExStudent student: variable().getStudents()) {
+            if (student.getContext(assignment).nrExams(getPeriod().getIndex(), exam)>0) conflicts++;
+        }
         return conflicts;
     }
 
@@ -119,13 +121,14 @@ public int twoInADayPenalty(Assignment<ExExam, ExPlacement> assignment) {
         if (!prev && !next) return 0;
         int penalty = 0;
         for (ExStudent student: variable().getStudents()) {
-            if (m.areDirectConflictsAllowed() && student.nrExams(assignment, getPeriod(), exam)>0) continue;
+        	ExStudent.Context cx = student.getContext(assignment);
+            if (m.areDirectConflictsAllowed() && cx.nrExams(getPeriod().getIndex(), exam)>0) continue;
             if (prev) 
                 for (ExPeriod p=prevPeriod;p!=null && p.getDay()==getPeriod().getDay();p=p.prev())
-                    if (student.hasExam(assignment, p,exam)) penalty++;
+                    if (cx.hasExam(p.getIndex(), exam)) penalty++;
             if (next)
                 for (ExPeriod p=nextPeriod;p!=null && p.getDay()==getPeriod().getDay();p=p.next())
-                    if (student.hasExam(assignment, p,exam)) penalty++; 
+                    if (cx.hasExam(p.getIndex(), exam)) penalty++; 
         }
         return penalty;
     }
@@ -136,11 +139,13 @@ public int widerSpreadPenalty(Assignment<ExExam, ExPlacement> assignment) {
         ExModel m = (ExModel)exam.getModel();
         int penalty = 0;
         for (ExStudent student: variable().getStudents()) {
-            if (m.areDirectConflictsAllowed() && student.nrExams(assignment, getPeriod(), exam)>0) continue;
+        	ExStudent.Context cx = student.getContext(assignment);
+        	
+            if (m.areDirectConflictsAllowed() && cx.nrExams(getPeriod().getIndex(), exam)>0) continue;
             for (ExPeriod p=getPeriod().next();p!=null && p.getIndex()-getPeriod().getIndex()<=m.getPeriodSpreadLength(); p=p.next())
-                if (student.hasExam(assignment, p,exam)) penalty++;
+                if (cx.hasExam(p.getIndex(), exam)) penalty++;
             for (ExPeriod p=getPeriod().prev();p!=null && getPeriod().getIndex()-p.getIndex()<=m.getPeriodSpreadLength(); p=p.prev())
-                if (student.hasExam(assignment, p,exam)) penalty++;
+                if (cx.hasExam(p.getIndex(), exam)) penalty++;
         }
         return penalty;
     }
@@ -158,9 +163,10 @@ private int combinedPenalty(Assignment<ExExam, ExPlacement> assignment) {
         boolean next2 = nextPeriod2!=null && getPeriod().getDay()==nextPeriod2.getDay(); 
         int penalty = 0;
         for (ExStudent student: variable().getStudents()) {
+        	ExStudent.Context cx = student.getContext(assignment);
 
             if (m.areDirectConflictsAllowed()) {
-                Set<ExExam> exams = student.getExams(assignment, getPeriod());
+                Set<ExExam> exams = cx.getExams(getPeriod().getIndex());
                 int nrExams = exams.size() + (exams.contains(exam)?0:1);
                 if (nrExams>1) {
                     penalty+=m.getDirectConflictWeight();
@@ -169,19 +175,19 @@ private int combinedPenalty(Assignment<ExExam, ExPlacement> assignment) {
             }
 
             for (ExPeriod p=getPeriod().next();p!=null && p.getIndex()-getPeriod().getIndex()<=m.getPeriodSpreadLength(); p=p.next())
-                if (student.hasExam(assignment, p,exam)) penalty++;
+                if (cx.hasExam(p.getIndex(), exam)) penalty++;
             for (ExPeriod p=getPeriod().prev();p!=null && getPeriod().getIndex()-p.getIndex()<=m.getPeriodSpreadLength(); p=p.prev())
-                if (student.hasExam(assignment, p,exam)) penalty++;
+                if (cx.hasExam(p.getIndex(), exam)) penalty++;
             
-            if (prev && student.hasExam(assignment, prevPeriod,exam)) penalty+=m.getTwoInARowWeight();
-            if (next && student.hasExam(assignment, nextPeriod,exam)) penalty+=m.getTwoInARowWeight();
+            if (prev && cx.hasExam(prevPeriod.getIndex(), exam)) penalty+=m.getTwoInARowWeight();
+            if (next && cx.hasExam(nextPeriod.getIndex(), exam)) penalty+=m.getTwoInARowWeight();
 
             if (prev2) 
                 for (ExPeriod p=prevPeriod2;p!=null && p.getDay()==getPeriod().getDay();p=p.prev())
-                    if (student.hasExam(assignment, p,exam)) penalty+=m.getTwoInADayWeight(); 
+                    if (cx.hasExam(p.getIndex(), exam)) penalty+=m.getTwoInADayWeight(); 
             if (next2)
                 for (ExPeriod p=nextPeriod2;p!=null && p.getDay()==getPeriod().getDay();p=p.next())
-                    if (student.hasExam(assignment, p,exam)) penalty+=m.getTwoInADayWeight();
+                    if (cx.hasExam(p.getIndex(), exam)) penalty+=m.getTwoInADayWeight();
         }
         return penalty;
     }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExRoom.java b/src/net/sf/cpsolver/itc/exam/model/ExRoom.java
index f0457c6..e62dd35 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExRoom.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExRoom.java
@@ -1,11 +1,15 @@
 package net.sf.cpsolver.itc.exam.model;
 
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 import java.util.TreeSet;
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.assignment.context.ConstraintWithContext;
 import org.cpsolver.ifs.model.ConstraintListener;
 
@@ -33,7 +37,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class ExRoom extends ConstraintWithContext<ExExam, ExPlacement, ExRoom.Context> {
+public class ExRoom extends ConstraintWithContext<ExExam, ExPlacement, ExRoom.Context> implements CanInheritContext<ExExam, ExPlacement, ExRoom.Context> {
     private int iSize;
     private int iPenalty;
     
@@ -76,6 +80,12 @@ public void computeConflicts(Assignment<ExExam, ExPlacement> assignment, ExPlace
     	Context context = getContext(assignment);
         if (p.getRoom().equals(this)) {
             ExExam ex = p.variable();
+            /*
+            if (ex.getStudents().size() > getSize())  {
+            	conflicts.add(p);
+            	return;
+            }
+            */
             if (ex.isRoomExclusive() || context.isExclusive(p.getPeriodIndex())) {
                 conflicts.addAll(context.getExams(p.getPeriodIndex()));
                 return;
@@ -99,6 +109,7 @@ public void computeConflicts(Assignment<ExExam, ExPlacement> assignment, ExPlace
                         if (adeptDiff==0) break;
                     } 
                 }
+                if (adept == null) break;
                 adepts.remove(adept);
                 rem += ((ExExam)adept.variable()).getStudents().size();
                 conflicts.add(adept);
@@ -112,6 +123,7 @@ public void computeConflicts(Assignment<ExExam, ExPlacement> assignment, ExPlace
     public boolean inConflict(Assignment<ExExam, ExPlacement> assignment, ExPlacement p) {
         if (!p.getRoom().equals(this)) return false;
         ExExam ex = p.variable();
+        // if (ex.getStudents().size() > getSize()) return true;
         Context context = getContext(assignment);
         return (
                 context.isExclusive(p.getPeriodIndex()) || 
@@ -278,23 +290,39 @@ private Context(ExModel m, Assignment<ExExam, ExPlacement> assignment) {
     			if (value.getRoom().equals(ExRoom.this))
     				assigned(assignment, value);
     	}
+    	
+    	@SuppressWarnings("unchecked")
+		private Context(ExModel m, Assignment<ExExam, ExPlacement> assignment, Context parent) {
+            synchronized (parent.iExams) {
+                iUsedSpace = Arrays.copyOf(parent.iUsedSpace, m.getNrPeriods());
+                iExclusive = Arrays.copyOf(parent.iExclusive, m.getNrPeriods());
+                iExams = new HashSet[m.getNrPeriods()];
+                for (int i = 0; i < m.getNrPeriods(); i++) {
+                    iExams[i] = new HashSet<ExPlacement>(parent.iExams[i]);
+                }
+			}
+    	}
 
 		@Override
 		public void assigned(Assignment<ExExam, ExPlacement> assignment, ExPlacement p) {
-	        iExams[p.getPeriodIndex()].add(p);
-	        iUsedSpace[p.getPeriodIndex()] += p.variable().getStudents().size();
-	        iExclusive[p.getPeriodIndex()] = p.variable().isRoomExclusive();
+			synchronized (iExams) {
+				iExams[p.getPeriodIndex()].add(p);
+				iUsedSpace[p.getPeriodIndex()] += p.variable().getStudents().size();
+				iExclusive[p.getPeriodIndex()] = p.variable().isRoomExclusive();
+			}
 		}
 
 		@Override
 		public void unassigned(Assignment<ExExam, ExPlacement> assignment, ExPlacement p) {
-	        iExams[p.getPeriodIndex()].remove(p);
-	        iUsedSpace[p.getPeriodIndex()] -= p.variable().getStudents().size();
-	        iExclusive[p.getPeriodIndex()] = false;
+			synchronized (iExams) {
+				iExams[p.getPeriodIndex()].remove(p);
+				iUsedSpace[p.getPeriodIndex()] -= p.variable().getStudents().size();
+				iExclusive[p.getPeriodIndex()] = false;
+			}
 		}
 		
 		public int getUsedSpace(int period) {
-			return iUsedSpace[period];
+			return Math.max(0, iUsedSpace[period]);
 		}
 
 		public boolean isExclusive(int period) {
@@ -304,11 +332,23 @@ public boolean isExclusive(int period) {
 		public Set<ExPlacement> getExams(int period) {
 			return iExams[period];
 		}
-}
+		
+		public List<ExExam> getExaminations(int period) {
+			List<ExExam> exams = new ArrayList<ExExam>(iExams[period].size());
+			for (ExPlacement p: getExams(period))
+				exams.add(p.variable());
+			return exams;
+		}
+    }
 
 	@Override
 	public Context createAssignmentContext(Assignment<ExExam, ExPlacement> assignment) {
 		return new Context((ExModel)getModel(), assignment);
 	}
+
+	@Override
+	public Context inheritAssignmentContext(Assignment<ExExam, ExPlacement> assignment, Context parentContext) {
+		return new Context((ExModel)getModel(), assignment, parentContext);
+	}
     
 }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExStudent.java b/src/net/sf/cpsolver/itc/exam/model/ExStudent.java
index 655718a..a085d81 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExStudent.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExStudent.java
@@ -47,41 +47,71 @@ public ExStudent(int id) {
     }
     
     /** List of exams that this student has at the given period */
-    public abstract Set<ExExam> getExams(Assignment<ExExam, ExPlacement> assignment, int period);
+    @Deprecated
+    public Set<ExExam> getExams(Assignment<ExExam, ExPlacement> assignment, int period) {
+    	return getContext(assignment).getExams(period);
+    }
+    
     /** List of exams that this student has at the given period */
+    @Deprecated
     public Set<ExExam> getExams(Assignment<ExExam, ExPlacement> assignment, ExPeriod period) {
-        return getExams(assignment, period.getIndex());
+    	return getContext(assignment).getExams(period.getIndex());
     }
+    
     /** List of exams that this student has at the given period */
     public String getExamStr(Assignment<ExExam, ExPlacement> assignment, ExPeriod period) {
         StringBuffer sb = new StringBuffer();
-        for (Iterator<ExExam> i=getExams(assignment, period.getIndex()).iterator();i.hasNext();) {
+        for (Iterator<ExExam> i=getContext(assignment).getExams(period.getIndex()).iterator();i.hasNext();) {
             sb.append(i.next().getId());
             sb.append(i.hasNext()?",":"");
         }
         return sb.toString();
     }
+    
     /** True, if this student has one or more exams at the given period */
-    public abstract boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period);
+    @Deprecated
+    public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period) {
+    	return getContext(assignment).hasExam(period);
+    }
     /** True, if this student has one or more exams at the given period */
+    @Deprecated
     public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, ExPeriod period) {
-        return hasExam(assignment, period.getIndex());
+    	return getContext(assignment).hasExam(period.getIndex());
     }
     /** True, if this student has one or more exams at the given period (given exam excluded) */
-    public abstract boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude);
+    @Deprecated
+    public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude) {
+    	return getContext(assignment).hasExam(period, exclude);
+    }
+    
     /** True, if this student has one or more exams at the given period (given exam excluded) */
+    @Deprecated
     public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, ExPeriod period, ExExam exclude) {
-        return hasExam(assignment, period.getIndex(), exclude);
+    	return getContext(assignment).hasExam(period.getIndex(), exclude);
     }
+    
     /** Number of exams that this student has at the given period */
-    public abstract int nrExams(Assignment<ExExam, ExPlacement> assignment, int period);
+    @Deprecated
+    public int nrExams(Assignment<ExExam, ExPlacement> assignment, int period) {
+    	return getContext(assignment).nrExams(period);
+    }
+    
     /** Number of exams that this student has at the given period */
-    public int nrExams(Assignment<ExExam, ExPlacement> assignment, ExPeriod period) { return nrExams(assignment, period.getIndex()); }
+    @Deprecated
+    public int nrExams(Assignment<ExExam, ExPlacement> assignment, ExPeriod period) {
+    	return getContext(assignment).nrExams(period.getIndex());
+    }
+    
     /** Number of exams that this student has at the given period (given exam excluded) */
-    public abstract int nrExams(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude);
+    @Deprecated
+    public int nrExams(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude) {
+    	return getContext(assignment).nrExams(period, exclude);
+    }
+    
     /** Number of exams that this student has at the given period (given exam excluded) */
+    @Deprecated
     public int nrExams(Assignment<ExExam, ExPlacement> assignment, ExPeriod period, ExExam exclude) {
-        return nrExams(assignment, period.getIndex(), exclude);
+    	return getContext(assignment).nrExams(period.getIndex(), exclude);
     }
 
     /** 
@@ -192,7 +222,10 @@ public int getNrDirectConflicts(Assignment<ExExam, ExPlacement> assignment) {
     
     public interface Context extends AssignmentConstraintContext<ExExam, ExPlacement> {
     	public ExPlacement getPlacement(int period);
+    	public boolean hasExam(int period);
+    	public boolean hasExam(int period, ExExam exclude);
     	public Set<ExExam> getExams(int period);
 		public int nrExams(int period);
+    	public int nrExams(int period, ExExam exclude);
     }
 }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExStudentHard.java b/src/net/sf/cpsolver/itc/exam/model/ExStudentHard.java
index 82c5d90..7dc09a4 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExStudentHard.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExStudentHard.java
@@ -1,9 +1,11 @@
 package net.sf.cpsolver.itc.exam.model;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.model.ConstraintListener;
 
 /**
@@ -30,7 +32,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class ExStudentHard extends ExStudent {
+public class ExStudentHard extends ExStudent implements CanInheritContext<ExExam, ExPlacement, ExStudentHard.Context> {
     
     /**
      * Constructor
@@ -98,34 +100,7 @@ public ExPlacement getPlacement(Assignment<ExExam, ExPlacement> assignment, int
     public ExPlacement getPlacement(Assignment<ExExam, ExPlacement> assignment, ExPeriod period) {
         return getPlacement(assignment, period.getIndex());
     }
-    /**
-     * Return exams that are assigned to the given period
-     */
-    public Set<ExExam> getExams(Assignment<ExExam, ExPlacement> assignment, int period) {
-        Set<ExExam> set = new HashSet<ExExam>();
-        ExPlacement p = getPlacement(assignment, period);
-        if (p != null) set.add(p.variable());
-        return set;
-    }
-    
-    /** True, if this student has one or more exams at the given period */
-    public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period) {
-    	return getPlacement(assignment, period) != null;
-    }
-    /** True, if this student has one or more exams at the given period (given exam excluded) */
-    public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude) {
-    	ExPlacement p = getPlacement(assignment, period);
-    	return p != null && !p.variable().equals(exclude);
-    }
-    /** Number of exams that this student has at the given period */
-    public int nrExams(Assignment<ExExam, ExPlacement> assignment, int period) {
-        return (hasExam(assignment, period)?1:0);
-    }
-    /** Number of exams that this student has at the given period (given exam excluded)*/
-    public int nrExams(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude) {
-        return (hasExam(assignment, period,exclude)?1:0);
-    }
-    
+
     public class Context implements ExStudent.Context {
         private ExPlacement[] iTable = null;
         
@@ -140,6 +115,10 @@ private Context(ExModel m, Assignment<ExExam, ExPlacement> assignment) {
                 		assigned(assignment, p);
                 }
         }
+        
+        private Context(ExModel m, Assignment<ExExam, ExPlacement> assignment, Context parent) {
+        	iTable = Arrays.copyOf(parent.iTable, m.getNrPeriods());
+        }
 
 		@Override
 		public void assigned(Assignment<ExExam, ExPlacement> assignment, ExPlacement p) {
@@ -167,10 +146,32 @@ public Set<ExExam> getExams(int period) {
 		public int nrExams(int period) {
 			return iTable[period] != null ? 1 : 0;
 		}
+
+		@Override
+		public boolean hasExam(int period) {
+			return iTable[period] != null;
+		}
+
+		@Override
+		public boolean hasExam(int period, ExExam exclude) {
+			ExPlacement p = iTable[period];
+	    	return p != null && !p.variable().equals(exclude);
+		}
+
+		@Override
+		public int nrExams(int period, ExExam exclude) {
+			ExPlacement p = iTable[period];
+			return p != null && !p.variable().equals(exclude) ? 1 : 0;
+		}
     }
 
 	@Override
 	public Context createAssignmentContext(Assignment<ExExam, ExPlacement> assignment) {
 		return new Context((ExModel)getModel(), assignment);
 	}
+
+	@Override
+	public Context inheritAssignmentContext(Assignment<ExExam, ExPlacement> assignment, Context parentContext) {
+		return new Context((ExModel)getModel(), assignment, parentContext);
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/exam/model/ExStudentSoft.java b/src/net/sf/cpsolver/itc/exam/model/ExStudentSoft.java
index 2f31254..557d18b 100644
--- a/src/net/sf/cpsolver/itc/exam/model/ExStudentSoft.java
+++ b/src/net/sf/cpsolver/itc/exam/model/ExStudentSoft.java
@@ -1,9 +1,11 @@
 package net.sf.cpsolver.itc.exam.model;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 
 /**
  * Representation of a student. Direct student conflicts are allowed
@@ -29,7 +31,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class ExStudentSoft extends ExStudent {
+public class ExStudentSoft extends ExStudent implements CanInheritContext<ExExam, ExPlacement, ExStudentSoft.Context> {
     
     /**
      * Constructor
@@ -73,31 +75,6 @@ public void afterUnassigned(Assignment<ExExam, ExPlacement> assignment, long ite
     	getContext(assignment).unassigned(assignment, p);
     }
     
-    /** List of exams that this student has at the given period */
-    public Set<ExExam> getExams(Assignment<ExExam, ExPlacement> assignment, int period) {
-        return getContext(assignment).getExams(period);
-    }
-    /** True, if this student has one or more exams at the given period */
-    public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period) {
-        return getContext(assignment).nrExams(period) > 0;
-    }
-    /** Number of exams that this student has at the given period */
-    public int nrExams(Assignment<ExExam, ExPlacement> assignment, int period) {
-        return getContext(assignment).nrExams(period);
-    }
-    /** True, if this student has one or more exams at the given period (given exam excluded)*/
-    public boolean hasExam(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude) {
-        if (exclude == null) return hasExam(assignment, period);
-        ExStudent.Context context = getContext(assignment);
-        return (context.nrExams(period) > (context.getExams(period).contains(exclude) ? 1 : 0));
-    }
-    /** Number of exams that this student has at the given period (given exam excluded)*/
-    public int nrExams(Assignment<ExExam, ExPlacement> assignment, int period, ExExam exclude) {
-        if (exclude == null) return nrExams(assignment, period);
-        ExStudent.Context context = getContext(assignment);
-        return context.nrExams(period) - (context.getExams(period).contains(exclude) ? 1 : 0);
-    }
-    
     public void assigned(long iteration, ExPlacement value) {
     }
         
@@ -123,17 +100,32 @@ private Context(ExModel m, Assignment<ExExam, ExPlacement> assignment) {
                 		assigned(assignment, p);
                 }
     	}
+    	
+    	@SuppressWarnings("unchecked")
+		private Context(ExModel m, Assignment<ExExam, ExPlacement> assignment, Context parent) {
+    		synchronized (parent.iExams) {
+        		iNrExams = Arrays.copyOf(parent.iNrExams, m.getNrPeriods());
+                iExams = new HashSet[m.getNrPeriods()];
+                for (int i=0;i<m.getNrPeriods();i++) {
+                    iExams[i]=new HashSet<ExExam>(parent.iExams[i]);
+                }
+			}
+    	}
 
 		@Override
 		public void assigned(Assignment<ExExam, ExPlacement> assignment, ExPlacement p) {
-	        if (iExams[p.getPeriodIndex()].add(p.variable()))
-	            iNrExams[p.getPeriodIndex()]++;
+			synchronized (iExams) {
+		        if (iExams[p.getPeriodIndex()].add(p.variable()))
+		            iNrExams[p.getPeriodIndex()]++;
+			}
 		}
 
 		@Override
 		public void unassigned(Assignment<ExExam, ExPlacement> assignment, ExPlacement p) {
-	        if (iExams[p.getPeriodIndex()].remove(p.variable()))
-	            iNrExams[p.getPeriodIndex()]--;
+			synchronized (iExams) {
+				if (iExams[p.getPeriodIndex()].remove(p.variable()))
+					iNrExams[p.getPeriodIndex()]--;
+			}
 		}
 		
 		@Override
@@ -150,6 +142,23 @@ public int nrExams(int period) {
 		public ExPlacement getPlacement(int period) {
 			return null;
 		}
+
+		@Override
+		public boolean hasExam(int period) {
+			return iNrExams[period] > 0;
+		}
+
+		@Override
+		public boolean hasExam(int period, ExExam exclude) {
+			if (exclude == null) return iNrExams[period] > 0;
+	        return (iNrExams[period] > (iExams[period].contains(exclude) ? 1 : 0));
+		}
+
+		@Override
+		public int nrExams(int period, ExExam exclude) {
+			if (exclude == null) return iNrExams[period];
+	        return (iExams[period].contains(exclude) ? iNrExams[period] - 1 : iNrExams[period]);
+		}
     }
 
 	@Override
@@ -157,4 +166,9 @@ public Context createAssignmentContext(Assignment<ExExam, ExPlacement> assignmen
 		return new Context((ExModel)getModel(), assignment);
 	}
 
+	@Override
+	public Context inheritAssignmentContext(Assignment<ExExam, ExPlacement> assignment, Context parentContext) {
+		return new Context((ExModel)getModel(), assignment, parentContext);
+	}
+
 }
diff --git a/src/net/sf/cpsolver/itc/heuristics/ItcNeighbourSelection.java b/src/net/sf/cpsolver/itc/heuristics/ItcNeighbourSelection.java
index 025a590..865faa1 100644
--- a/src/net/sf/cpsolver/itc/heuristics/ItcNeighbourSelection.java
+++ b/src/net/sf/cpsolver/itc/heuristics/ItcNeighbourSelection.java
@@ -16,7 +16,6 @@
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
 
-import net.sf.cpsolver.itc.ItcModel;
 import net.sf.cpsolver.itc.heuristics.search.ItcHillClimber;
 import net.sf.cpsolver.itc.heuristics.search.ItcTabuSearch;
 import net.sf.cpsolver.itc.heuristics.search.ItcGreatDeluge;
@@ -118,27 +117,30 @@ public void init(Solver<V,T> solver) {
     /** Neighbour selection  -- based on the phase, construction strategy is used first,
      * than it iterates between two or three given neighbour selections*/
     public Neighbour<V,T> selectNeighbour(Solution<V,T> solution) {
-        Neighbour<V,T> n = null;
+    	if (!solution.isComplete() && solution.getModel().getBestUnassignedVariables() == 0)
+    		return iConstruct.selectNeighbour(solution);
+        
+    	Neighbour<V,T> n = null;
         Phase phase = getContext(solution.getAssignment());
         switch (phase.getPhase()) {
             case 0 :
                 n = iConstruct.selectNeighbour(solution);
                 if (n!=null) return n;
-                phase.incPhase(solution, "first");
+                phase.setPhase(1, solution, "one");
             case 1 :
                 n = iFirst.selectNeighbour(solution);
                 if (n!=null) return n;
-                phase.incPhase(solution, "second");
+                phase.setPhase(2, solution, "two");
             case 2 :
                 n = iSecond.selectNeighbour(solution);
                 if (n!=null) return n;
-                phase.incPhase(solution, "third");
+                phase.setPhase(3, solution, "three");
             case 3 :
                 n = (iThird==null?null:iThird.selectNeighbour(solution));
                 if (n!=null) return n;
-                phase.incPhase(solution, "first");
+                phase.setPhase(4, solution, "one");
             default :
-            	phase.setPhase(1);
+            	phase.setPhase(1, solution, "one");
                 return selectNeighbour(solution);
         }
     }
@@ -151,18 +153,14 @@ public int getPhase() {
 		}
 		
 		/** Change phase, i.e., what selector is to be used next */
-		public void incPhase(Solution<V,T> solution, String name) {
-	        iPhase ++;
+		public synchronized void setPhase(int phase, Solution<V,T> solution, String name) {
+			if (iPhase == phase) return;
+	        iPhase = phase;
 	        if (sLog.isInfoEnabled()) {
-	            ItcModel<V,T> m = (ItcModel<V,T>)solution.getModel();
-	            sLog.info("**CURR["+solution.getIteration()+"]** P:"+Math.round(m.getTotalValue(solution.getAssignment()))+" ("+m.csvLine(solution.getAssignment())+")");
+	            sLog.info("**CURR["+solution.getIteration()+"]** " + solution);
 	            sLog.info("Phase "+name);
 	        }
 		}
-		
-		public void setPhase(int phase) {
-			iPhase = phase;
-		}
     }
 
 	@Override
diff --git a/src/net/sf/cpsolver/itc/heuristics/ItcUnassignedVariableSelection.java b/src/net/sf/cpsolver/itc/heuristics/ItcUnassignedVariableSelection.java
index 7fd013d..bf8ac4d 100644
--- a/src/net/sf/cpsolver/itc/heuristics/ItcUnassignedVariableSelection.java
+++ b/src/net/sf/cpsolver/itc/heuristics/ItcUnassignedVariableSelection.java
@@ -1,6 +1,10 @@
 package net.sf.cpsolver.itc.heuristics;
 
+import java.lang.reflect.Array;
+import java.util.Collection;
+
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.InheritedAssignment;
 import org.cpsolver.ifs.heuristics.VariableSelection;
 import org.cpsolver.ifs.model.Model;
 import org.cpsolver.ifs.model.Value;
@@ -8,6 +12,7 @@
 import org.cpsolver.ifs.solution.Solution;
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
+import org.cpsolver.ifs.util.ToolBox;
 
 /**
  * Unassigned variable selection. The "biggest" variable (using {@link Variable#compareTo(Object)})
@@ -44,13 +49,41 @@ public void init(Solver<V,T> solver) {}
     
     /** Variable selection */
     public V selectVariable(Solution<V,T> solution) {
-        Model<V,T> model = solution.getModel();
+    	Model<V,T> model = solution.getModel();
         Assignment<V, T> assignment = solution.getAssignment();
-        if (assignment.nrAssignedVariables() == model.variables().size()) return null; 
-        V variable = null;
-        for (V v: assignment.unassignedVariables(model)) {
-            if (variable==null || v.compareTo(variable)<0) variable = v;
+        if (assignment.nrAssignedVariables() == model.variables().size()) return null;
+        int index = solution.getAssignment().getIndex();
+        Collection<V> unassigned = assignment.unassignedVariables(model);
+        if (solution.getAssignment() instanceof InheritedAssignment) {
+            if (index < 0 || unassigned.size() < index) {
+            	return ToolBox.random(unassigned);
+            } else if (index <= 1) {
+                V variable = null;
+                for (V v: unassigned) {
+                    if (variable==null || v.compareTo(variable)<0) variable = v;
+                }
+                return variable;
+            } else {
+            	@SuppressWarnings("unchecked")
+    			V[] adepts = (V[])Array.newInstance(Variable.class, index);
+            	for (V v: unassigned) {
+            		for (int i = 0; i < adepts.length; i++) {
+            			V x = adepts[i];
+            			if (x == null) {
+            				adepts[i] = v; break;
+            			} else if (v.compareTo(x) < 0) {
+            				adepts[i] = v; v = x;
+            			}
+            		}
+            	}
+            	return adepts[index - 1];
+            }        	
+        } else {
+            V variable = null;
+            for (V v: unassigned) {
+                if (variable==null || v.compareTo(variable)<0) variable = v;
+            }
+            return variable;
         }
-        return variable;
     }
 }
diff --git a/src/net/sf/cpsolver/itc/heuristics/neighbour/ItcLazyNeighbour.java b/src/net/sf/cpsolver/itc/heuristics/neighbour/ItcLazyNeighbour.java
deleted file mode 100644
index 0d7ebfe..0000000
--- a/src/net/sf/cpsolver/itc/heuristics/neighbour/ItcLazyNeighbour.java
+++ /dev/null
@@ -1,86 +0,0 @@
-package net.sf.cpsolver.itc.heuristics.neighbour;
-
-import org.cpsolver.ifs.assignment.Assignment;
-import org.cpsolver.ifs.model.Neighbour;
-import org.cpsolver.ifs.model.Value;
-import org.cpsolver.ifs.model.Variable;
-import net.sf.cpsolver.itc.ItcModel;
-
-/**
- * Lazy neigbour (a change of the overall solution value is unknown before
- * the neighbour is assigned, it is possible to undo the neighbour instead). 
- * This neighbour is useful when it is 
- * two expensive to compute change of overall solution value before the 
- * variable is reassigned. It is possible to undo the neighbour instead.
- * Search strategy has to implement {@link LazyNeighbourAcceptanceCriterion}.
- *  
- * @version
- * ITC2007 1.0<br>
- * Copyright (C) 2007 Tomas Muller<br>
- * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
- * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
- * <br>
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 3 of the License, or (at your option) any later version.
- * <br><br>
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- * <br><br>
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not see
- * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
- */
-public abstract class ItcLazyNeighbour<V extends Variable<V, T>, T extends Value<V, T>> implements Neighbour<V,T> {
-    private LazyNeighbourAcceptanceCriterion<V,T> iCriterion = null;
-    
-    /**
-     * Set acceptance criterion (to be used by a search strategy before the 
-     * neighbour is accepted, so that it can be undone if desired)  
-     */
-    public void setAcceptanceCriterion(LazyNeighbourAcceptanceCriterion<V,T> criterion) {
-        iCriterion = criterion;
-    }
-    
-    /**
-     * Assign neighbour, check given acceptance criterion, and undo
-     * assignment if the change is not accepted. 
-     */
-    public void assign(Assignment<V, T> assignment, long iteration) {
-        double before = getModel().getTotalValue(assignment);
-        doAssign(assignment, iteration);
-        double after = getModel().getTotalValue(assignment);
-        if (!iCriterion.accept(assignment, this, after - before)) undoAssign(assignment, iteration);
-    }
-    /**
-     * Return -1 (neighbour is always accepted). The search strategy that
-     * is using this neighbour must implement {@link LazyNeighbourAcceptanceCriterion}.
-     */
-    public double value(Assignment<V, T> assignment) { return -1; }
-    
-    /** Perform assignment */
-    protected abstract void doAssign(Assignment<V, T> assignment, long iteration);
-    /** Undo assignment */
-    protected abstract void undoAssign(Assignment<V, T> assignment, long iteration);
-    /** Return problem model (it is needed in order to be able to get
-     * overall solution value before and after the assignment of this neighbour) */
-    public abstract ItcModel<V,T> getModel();
-    
-    /** Neighbour acceptance criterion interface (to be implemented
-     * by search strategies that are using {@link ItcLazyNeighbour}. 
-     * It is also required to call {@link ItcLazyNeighbour#setAcceptanceCriterion(net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion)}
-     * before the neighbour is accepted by the search strategy. 
-     */ 
-    public static interface LazyNeighbourAcceptanceCriterion<V extends Variable<V, T>, T extends Value<V, T>> {
-        /** True when the currently assigned neighbour should be accepted (false means
-         * that the change will be undone
-         * @param neighbour neighbour that was assigned
-         * @param value change in overall solution value
-         * @return true if the neighbour can be accepted (false to undo the assignment)
-         */
-        public boolean accept(Assignment<V, T> assignment, ItcLazyNeighbour<V,T> neighbour, double value);
-    }
-}
diff --git a/src/net/sf/cpsolver/itc/heuristics/neighbour/ItcLazySwap.java b/src/net/sf/cpsolver/itc/heuristics/neighbour/ItcLazySwap.java
deleted file mode 100644
index 6584c91..0000000
--- a/src/net/sf/cpsolver/itc/heuristics/neighbour/ItcLazySwap.java
+++ /dev/null
@@ -1,82 +0,0 @@
-package net.sf.cpsolver.itc.heuristics.neighbour;
-
-import java.util.HashMap;
-import java.util.Map;
-
-import org.cpsolver.ifs.assignment.Assignment;
-import org.cpsolver.ifs.model.Value;
-import org.cpsolver.ifs.model.Variable;
-import net.sf.cpsolver.itc.ItcModel;
-
-/**
- * Lazy swap of two variables. See {@link ItcLazyNeighbour}.
- *  
- * @version
- * ITC2007 1.0<br>
- * Copyright (C) 2007 Tomas Muller<br>
- * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
- * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
- * <br>
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 3 of the License, or (at your option) any later version.
- * <br><br>
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- * <br><br>
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not see
- * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
- */
-public class ItcLazySwap<V extends Variable<V, T>, T extends Value<V, T>> extends ItcLazyNeighbour<V, T> {
-    private T iV1, iV2, iOldV1, iOldV2; 
-    
-    /**
-     * Constructor
-     * @param v1 first variable
-     * @param v2 second variable
-     */
-    public ItcLazySwap(Assignment<V, T> assignment, T v1, T v2) {
-        iV1 = v1;
-        iV2 = v2;
-        iOldV1 = assignment.getValue(v1.variable());
-        iOldV2 = assignment.getValue(v2.variable());
-    }
-    
-    /** Perform swap */
-    protected void doAssign(Assignment<V, T> assignment, long iteration) {
-    	iOldV1 = assignment.unassign(iteration, iV1.variable());
-    	iOldV2 = assignment.unassign(iteration, iV2.variable());
-    	assignment.assign(iteration, iV1);
-    	assignment.assign(iteration, iV2);
-    }
-    
-    /** Undo the swap */
-    protected void undoAssign(Assignment<V, T> assignment, long iteration) {
-    	assignment.unassign(iteration, iV1.variable());
-    	assignment.unassign(iteration, iV2.variable());
-    	if (iOldV1 != null) assignment.assign(iteration, iOldV1);
-    	if (iOldV2 != null) assignment.assign(iteration, iOldV2);
-    }
-    /** Return problem model */
-    public ItcModel<V,T> getModel() {
-        return (ItcModel<V,T>)iV1.variable().getModel();
-    }
-    
-    /** String representation */
-    public String toString() {
-        return "Lazy " + iOldV1 + " -> " + iV1 + ", " + iOldV2 + " -> " + iV2;
-    }
-
-	@Override
-	public Map<V, T> assignments() {
-		Map<V, T> ret = new HashMap<V, T>();
-		ret.put(iV1.variable(), iV1);
-		ret.put(iV2.variable(), iV2);
-		return ret;
-	}
-
-}
diff --git a/src/net/sf/cpsolver/itc/heuristics/search/ItcGreatDeluge.java b/src/net/sf/cpsolver/itc/heuristics/search/ItcGreatDeluge.java
index cd959bd..c4a781c 100644
--- a/src/net/sf/cpsolver/itc/heuristics/search/ItcGreatDeluge.java
+++ b/src/net/sf/cpsolver/itc/heuristics/search/ItcGreatDeluge.java
@@ -9,12 +9,13 @@
 import java.util.StringTokenizer;
 
 import org.apache.log4j.Logger;
-
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentContext;
 import org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext;
 import org.cpsolver.ifs.extension.Extension;
 import org.cpsolver.ifs.heuristics.NeighbourSelection;
+import org.cpsolver.ifs.model.LazyNeighbour;
+import org.cpsolver.ifs.model.LazyNeighbour.LazyNeighbourAcceptanceCriterion;
 import org.cpsolver.ifs.model.Model;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.model.Value;
@@ -24,10 +25,9 @@
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
 import org.cpsolver.ifs.util.ToolBox;
+
 import net.sf.cpsolver.itc.heuristics.ItcParameterWeightOscillation;
 import net.sf.cpsolver.itc.heuristics.ItcParameterWeightOscillation.OscillationListener;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion;
 import net.sf.cpsolver.itc.heuristics.neighbour.selection.ItcNotConflictingMove;
 import net.sf.cpsolver.itc.heuristics.neighbour.selection.ItcSwapMove;
 import net.sf.cpsolver.itc.heuristics.search.ItcHillClimber.NeighbourSelector;
@@ -201,14 +201,14 @@ private Neighbour<V,T> genMove(Solution<V,T> solution) {
     }
     
     private boolean accept(Solution<V,T> solution, Neighbour<V,T> neighbour) {
-        if (neighbour instanceof ItcLazyNeighbour) {
-            ((ItcLazyNeighbour<V,T>)neighbour).setAcceptanceCriterion(this);
+        if (neighbour instanceof LazyNeighbour) {
+            ((LazyNeighbour<V,T>)neighbour).setAcceptanceCriterion(this);
             return true;
         } else return (neighbour.value(solution.getAssignment())<=0 || solution.getModel().getTotalValue(solution.getAssignment())+neighbour.value(solution.getAssignment())<= getContext(solution.getAssignment()).getBound());
     }
     
     /** Implementation of {@link net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion} interface */
-    public boolean accept(Assignment<V,T> assignment, ItcLazyNeighbour<V,T> neighbour, double value) {
+    public boolean accept(Assignment<V,T> assignment, LazyNeighbour<V,T> neighbour, double value) {
         return (value <= 0 || neighbour.getModel().getTotalValue(assignment) <= getContext(assignment).getBound());
     }
     
@@ -262,7 +262,11 @@ protected void info(Solution<V,T> solution) {
             iAcceptedMoves = iMoves = 0;
         }
         
-        protected boolean incIter(Solution<V, T> solution) {
+        protected boolean canCheckBound(Solution<V, T> solution) {
+        	return !hasContextOverride() || solution.getAssignment().getIndex() <= 1;
+        }
+        
+        protected synchronized boolean incIter(Solution<V, T> solution) {
         	double best = solution.getModel().getBestValue();
             if (iIter < 0) {
                 iIter = 0; iLastImprovingIter = 0;
@@ -276,21 +280,25 @@ protected boolean incIter(Solution<V, T> solution) {
             if (sInfo && iIter % 100000 == 0) {
                 info(solution);
             }
-            if (iIter % 1000 == 0 && iBound > Math.max(best + 2.0, Math.pow(iUpperBoundRate, 1 + iNrIdle) * best)) {
-            	iBound = Math.max(best + 2.0, Math.pow(iUpperBoundRate, iNrIdle) * best);
-            	if (solution.getModel().getTotalValue(solution.getAssignment()) > iBound)
-            		solution.restoreBest();
-            }
-            if (iBound < Math.pow(iLowerBoundRate, 1 + iNrIdle) * best) {
-                iNrIdle++;
-                sLog.info(" -<["+iNrIdle+"]>- ");
-                iBound = Math.max(best + 2.0, Math.pow(iUpperBoundRate, iNrIdle) * best);
-                iAlterBound = iAlterBoundOnReheat;
-                if (iNextHeuristicsOnReheat) return true;
-            }
-            if (iAlterBound) {
-            	iBound = Math.max(best + 2.0, Math.pow(iUpperBoundRate, Math.max(1, iNrIdle)) * best);
-            	iAlterBound = false;
+            if (canCheckBound(solution)) {
+                if (iIter % 1000 == 0 && iBound > Math.max(best + 2.0, Math.pow(iUpperBoundRate, 1 + iNrIdle) * best)) {
+                	iBound = Math.max(best + 2.0, Math.pow(iUpperBoundRate, iNrIdle) * best);
+                	if (solution.getModel().getTotalValue(solution.getAssignment()) > iBound)
+                		solution.restoreBest();
+                }
+                if (iBound < Math.pow(iLowerBoundRate, 1 + iNrIdle) * best) {
+                    iNrIdle++;
+                    sLog.info(" -<["+iNrIdle+"]>- ");
+                    iBound = Math.max(best + 2.0, Math.pow(iUpperBoundRate, iNrIdle) * best);
+                    iAlterBound = iAlterBoundOnReheat;
+                    if (iNextHeuristicsOnReheat) return true;
+                }
+                if (iAlterBound) {
+                	iBound = Math.max(best + 2.0, Math.pow(iUpperBoundRate, Math.max(1, iNrIdle)) * best);
+                	//if (solution.getModel().getTotalValue(solution.getAssignment()) > iBound)
+                	//	solution.restoreBest();
+                	iAlterBound = false;
+                }
             }
             return false;
         }
diff --git a/src/net/sf/cpsolver/itc/heuristics/search/ItcHillClimber.java b/src/net/sf/cpsolver/itc/heuristics/search/ItcHillClimber.java
index bc043df..3b6ae08 100644
--- a/src/net/sf/cpsolver/itc/heuristics/search/ItcHillClimber.java
+++ b/src/net/sf/cpsolver/itc/heuristics/search/ItcHillClimber.java
@@ -12,6 +12,8 @@
 import org.cpsolver.ifs.assignment.context.AssignmentContext;
 import org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext;
 import org.cpsolver.ifs.heuristics.NeighbourSelection;
+import org.cpsolver.ifs.model.LazyNeighbour;
+import org.cpsolver.ifs.model.LazyNeighbour.LazyNeighbourAcceptanceCriterion;
 import org.cpsolver.ifs.model.Model;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.model.Value;
@@ -21,8 +23,7 @@
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
 import org.cpsolver.ifs.util.ToolBox;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion;
+
 import net.sf.cpsolver.itc.heuristics.neighbour.selection.ItcNotConflictingMove;
 import net.sf.cpsolver.itc.heuristics.neighbour.selection.ItcSwapMove;
 
@@ -161,8 +162,8 @@ public Neighbour<V,T> selectNeighbour(Solution<V,T> solution) {
             }
             Neighbour<V,T> n = ns.selectNeighbour(solution);
             if (n!=null) {
-                if (n instanceof ItcLazyNeighbour) {
-                    ((ItcLazyNeighbour<V,T>)n).setAcceptanceCriterion(this);
+                if (n instanceof LazyNeighbour) {
+                    ((LazyNeighbour<V,T>)n).setAcceptanceCriterion(this);
                     return n;
                 } else if (n.value(solution.getAssignment())<=0.0) return n;
             }
@@ -172,7 +173,7 @@ public Neighbour<V,T> selectNeighbour(Solution<V,T> solution) {
     }
     
     /** Implementation of {@link net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion} interface */
-    public boolean accept(Assignment<V,T> assignment, ItcLazyNeighbour<V,T> neighbour, double value) {
+    public boolean accept(Assignment<V,T> assignment, LazyNeighbour<V,T> neighbour, double value) {
         return value<=0;
     }
 
@@ -297,7 +298,7 @@ public class Context implements AssignmentContext {
         private int iLastImprovingIter = 0;
         private int iIter = 0;
         private long iT0 = -1;
-
+        
         public void reset() {
             iIter = 0;
             iLastImprovingIter = 0;
@@ -308,7 +309,7 @@ protected void setT0() {
             if (iT0 < 0) iT0 = System.currentTimeMillis();
         }
         
-        protected boolean incIter(Solution<V, T> solution) {
+        protected synchronized boolean incIter(Solution<V, T> solution) {
             iIter ++;
             if (iIter % 10000 == 0) {
                 if (sInfo) {
diff --git a/src/net/sf/cpsolver/itc/heuristics/search/ItcSimulatedAnnealing.java b/src/net/sf/cpsolver/itc/heuristics/search/ItcSimulatedAnnealing.java
index 8bf0c63..3a5398d 100644
--- a/src/net/sf/cpsolver/itc/heuristics/search/ItcSimulatedAnnealing.java
+++ b/src/net/sf/cpsolver/itc/heuristics/search/ItcSimulatedAnnealing.java
@@ -13,17 +13,18 @@
 import org.cpsolver.ifs.assignment.context.AssignmentContext;
 import org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext;
 import org.cpsolver.ifs.heuristics.NeighbourSelection;
+import org.cpsolver.ifs.model.LazyNeighbour;
 import org.cpsolver.ifs.model.Model;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.model.Value;
 import org.cpsolver.ifs.model.Variable;
+import org.cpsolver.ifs.model.LazyNeighbour.LazyNeighbourAcceptanceCriterion;
 import org.cpsolver.ifs.solution.Solution;
 import org.cpsolver.ifs.solution.SolutionListener;
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
 import org.cpsolver.ifs.util.ToolBox;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion;
+
 import net.sf.cpsolver.itc.heuristics.neighbour.selection.ItcRandomMove;
 import net.sf.cpsolver.itc.heuristics.neighbour.selection.ItcSwapMove;
 import net.sf.cpsolver.itc.heuristics.search.ItcHillClimber.NeighbourSelector;
@@ -227,8 +228,8 @@ private Neighbour<V,T> genMove(Solution<V,T> solution) {
     }
     
     private boolean accept(Solution<V,T> solution, Neighbour<V,T> neighbour) {
-        if (neighbour instanceof ItcLazyNeighbour) {
-            ((ItcLazyNeighbour<V,T>)neighbour).setAcceptanceCriterion(this);
+        if (neighbour instanceof LazyNeighbour) {
+            ((LazyNeighbour<V,T>)neighbour).setAcceptanceCriterion(this);
             return true;
         }
         Model<V,T> m = solution.getModel();
@@ -243,7 +244,7 @@ private boolean accept(Solution<V,T> solution, Neighbour<V,T> neighbour) {
     }
     
     /** Implementation of {@link net.sf.cpsolver.itc.heuristics.neighbour.ItcLazyNeighbour.LazyNeighbourAcceptanceCriterion} interface */
-    public boolean accept(Assignment<V,T> assignment, ItcLazyNeighbour<V,T> neighbour, double value) {
+    public boolean accept(Assignment<V,T> assignment, LazyNeighbour<V,T> neighbour, double value) {
         double prob = getContext(assignment).prob(value);
         if (prob>=1.0 || ToolBox.random()<prob) {
         	if (sInfo) getContext(assignment).accepted(value);
@@ -281,7 +282,7 @@ public class Context implements AssignmentContext {
         private long iLastReheatIter = 0;
         private long iLastCoolingIter = 0;
         private int iAcceptIter[] = new int[] {0,0,0};
-
+        
         private void cool(Solution<V,T> solution) {
             iTemperature *= iCoolingRate;
             if (sInfo) {
@@ -314,20 +315,26 @@ private void reheat(Solution<V,T> solution) {
             iLastReheatIter=iIter;
         }
         
-        private boolean incIter(Solution<V,T> solution) {
+        protected boolean canCoolOrRehear(Solution<V, T> solution) {
+        	return !hasContextOverride() || solution.getAssignment().getIndex() <= 1;
+        }
+        
+        private synchronized boolean incIter(Solution<V,T> solution) {
             if (iT0 < 0) {
             	iT0 = System.currentTimeMillis();
             	iTemperature = iInitialTemperature;
             }
             iIter++;
-            if (iIter > iLastImprovingIter + iRestoreBestLength) {
-            	restoreBest(solution);
-            }
-            if (iIter > Math.max(iLastReheatIter, iLastImprovingIter) + iReheatLength) {
-                reheat(solution);
-                return iNextHeuristicsOnReheat;
+            if (canCoolOrRehear(solution)) {
+                if (iIter > iLastImprovingIter + iRestoreBestLength) {
+                	restoreBest(solution);
+                }
+                if (iIter > Math.max(iLastReheatIter, iLastImprovingIter) + iReheatLength) {
+                    reheat(solution);
+                    return iNextHeuristicsOnReheat;
+                }
+                if (iIter > iLastCoolingIter + iTemperatureLength) cool(solution);
             }
-            if (iIter > iLastCoolingIter + iTemperatureLength) cool(solution);
             return false;
         }
         
diff --git a/src/net/sf/cpsolver/itc/heuristics/search/ItcTabuSearch.java b/src/net/sf/cpsolver/itc/heuristics/search/ItcTabuSearch.java
index 7fbc96d..137d883 100644
--- a/src/net/sf/cpsolver/itc/heuristics/search/ItcTabuSearch.java
+++ b/src/net/sf/cpsolver/itc/heuristics/search/ItcTabuSearch.java
@@ -6,9 +6,11 @@
 import java.util.Set;
 import java.util.TreeSet;
 
-import org.apache.log4j.Logger;
+import net.sf.cpsolver.itc.heuristics.neighbour.ItcSimpleNeighbour;
 
+import org.apache.log4j.Logger;
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.InheritedAssignment;
 import org.cpsolver.ifs.assignment.context.AssignmentContext;
 import org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext;
 import org.cpsolver.ifs.extension.ConflictStatistics;
@@ -17,7 +19,6 @@
 import org.cpsolver.ifs.heuristics.ValueSelection;
 import org.cpsolver.ifs.model.Model;
 import org.cpsolver.ifs.model.Neighbour;
-import org.cpsolver.ifs.model.SimpleNeighbour;
 import org.cpsolver.ifs.model.Value;
 import org.cpsolver.ifs.model.Variable;
 import org.cpsolver.ifs.solution.Solution;
@@ -112,6 +113,10 @@ public void init(Solver<V,T> solver) {
                 iStat = (ConflictStatistics<V,T>)extension;
     }
     
+    public void setValueWeight(double weight) {
+    	iValueWeight = weight;
+    }
+    
     /**
      * An element that is to be used to populate (and check) tabu list
      * @param value given value (to be assigned to its variable)
@@ -199,7 +204,7 @@ public Neighbour<V,T> selectNeighbour(Solution<V,T> solution) {
         if (tabu.size() > 0) 
             tabu.add(tabuElement(bestVal));
 
-        return new SimpleNeighbour<V,T>(bestVal.variable(), bestVal);        
+        return new ItcSimpleNeighbour<V,T>(solution.getAssignment(), bestVal.variable(), bestVal);        
     }
     
     /**
@@ -268,6 +273,12 @@ public T selectValue(Solution<V,T> solution, V variable) {
             sLog.debug("  [tabu] "+bestVal+" ("+(old==null?"":"was="+old+", ")+"val="+bestEval+(conflicts.isEmpty()?"":", conf="+(wconf+conflicts.size())+"/"+conflicts)+")");
         }
         
+        if (solution.getAssignment() instanceof InheritedAssignment && iStat != null) {
+        	for (T conflict: model.conflictValues(assignment, bestVal)) {
+        		iStat.variableUnassigned(solution.getIteration(), conflict, bestVal);
+        	}
+        }
+                
         if (tabu.size() > 0) tabu.add(tabuElement(bestVal));
         
         return bestVal;
diff --git a/src/net/sf/cpsolver/itc/tim/model/TTComp02Model.java b/src/net/sf/cpsolver/itc/tim/model/TTComp02Model.java
index 00a4fa9..7c4b138 100644
--- a/src/net/sf/cpsolver/itc/tim/model/TTComp02Model.java
+++ b/src/net/sf/cpsolver/itc/tim/model/TTComp02Model.java
@@ -7,12 +7,16 @@
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import java.util.StringTokenizer;
 
 import org.cpsolver.ifs.assignment.Assignment;
+import org.cpsolver.ifs.assignment.InheritedAssignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
+import org.cpsolver.ifs.solution.Solution;
 
 import net.sf.cpsolver.itc.ItcModel;
 
@@ -46,7 +50,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class TTComp02Model extends ItcModel<TimEvent, TimLocation> {
+public class TTComp02Model extends ItcModel<TimEvent, TimLocation> implements CanInheritContext<TimEvent, TimLocation, TTComp02Model.TTComp02Context>{
     /** Room constraints */
     protected List<TimRoom> iRooms = null;
     /** Student constraints */
@@ -259,6 +263,10 @@ public TTComp02Context(Assignment<TimEvent, TimLocation> assignment) {
     				assigned(assignment, location);
     		}
     	}
+    	
+    	public TTComp02Context(Assignment<TimEvent, TimLocation> assignment, TTComp02Context parent) {
+    		iScore = Arrays.copyOf(parent.iScore, 3);
+    	}
 
         /**
          * Update counters on assignment of an event
@@ -326,4 +334,14 @@ public AssignmentConstraintContext<TimEvent, TimLocation> createAssignmentContex
 	public Assignment<TimEvent, TimLocation> createAssignment(int index, Assignment<TimEvent, TimLocation> assignment) {
 		return new TimAssignment(this, index, assignment);
 	}
+	
+	@Override
+    public InheritedAssignment<TimEvent, TimLocation> createInheritedAssignment(Solution<TimEvent, TimLocation> solution, int index) {
+        return new TimInheritedAssignment(solution, index);
+    }
+
+	@Override
+	public TTComp02Context inheritAssignmentContext(Assignment<TimEvent, TimLocation> assignment, TTComp02Context parentContext) {
+		return new TTComp02Context(assignment, parentContext);
+	}
 }
\ No newline at end of file
diff --git a/src/net/sf/cpsolver/itc/tim/model/TimAssignment.java b/src/net/sf/cpsolver/itc/tim/model/TimAssignment.java
index d2189df..3283d6c 100644
--- a/src/net/sf/cpsolver/itc/tim/model/TimAssignment.java
+++ b/src/net/sf/cpsolver/itc/tim/model/TimAssignment.java
@@ -7,6 +7,7 @@
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.AssignmentAbstract;
+import org.cpsolver.ifs.assignment.context.AssignmentContextHolder;
 import org.cpsolver.ifs.assignment.context.DefaultParallelAssignmentContextHolder;
 import org.cpsolver.ifs.model.Model;
 
@@ -34,17 +35,28 @@
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
 public class TimAssignment extends AssignmentAbstract<TimEvent, TimLocation> {
-	private Model<TimEvent, TimLocation> iModel;
-	private int iIndex;
-	private int iNrAssigned = 0;
+	protected Model<TimEvent, TimLocation> iModel;
+	protected int iIndex;
+	protected int iNrAssigned = 0;
+	protected TimLocation[] iAssignment = null;
+	protected TimAssignment iParent = null;
 	
 	public TimAssignment(Model<TimEvent, TimLocation> model, int index, Assignment<TimEvent, TimLocation> assignment) {
 		super(new DefaultParallelAssignmentContextHolder<TimEvent, TimLocation>(index));
 		iIndex = index;
 		iModel = model;
-		if (assignment != null)
-            for (TimLocation value: assignment.assignedValues())
-                setValueInternal(0, value.variable(), value);
+		iParent = (TimAssignment) assignment;
+		if (iParent == null) {
+			iAssignment = new TimLocation[model.variables().size()];
+			iNrAssigned = 0;
+		} else {
+			iAssignment = Arrays.copyOf(((TimAssignment)iParent).toArray(), model.variables().size());
+			iNrAssigned = iParent.nrAssignedVariables();
+		}
+	}
+	
+	protected TimAssignment(AssignmentContextHolder<TimEvent, TimLocation> contextHolder) {
+		super(contextHolder);
 	}
 	
 	@Override
@@ -98,35 +110,14 @@ public Collection<TimEvent> assignedVariables() {
 		return assigned;
 	}
 
-    protected TimLocation[] getAssignments(TimEvent variable) {
-        synchronized (variable) {
-            TimLocation[] assignments = (TimLocation[])variable.getExtra();
-            if (assignments == null) {
-                assignments = (TimLocation[])new TimLocation[Math.max(10, 1 + iIndex)];
-                variable.setExtra(assignments);
-            } else if (assignments.length <= iIndex) {
-                assignments = Arrays.copyOf(assignments, 10 + iIndex);
-                variable.setExtra(assignments);
-            }
-            return assignments;
-        }
-    }
-    
 	@Override
-    @SuppressWarnings("deprecation")
     protected TimLocation getValueInternal(TimEvent variable) {
-    	if (iIndex == 1)
-    		return variable.getAssignment();
-        return getAssignments(variable)[iIndex];
+		return iAssignment[variable.getIndex()];
     }
     
 	@Override
-    @SuppressWarnings("deprecation")
     protected void setValueInternal(long iteration, TimEvent variable, TimLocation value) {
-    	if (iIndex == 1)
-    		variable.setAssignment(value);
-    	else
-    		getAssignments(variable)[iIndex] = value;
+		iAssignment[variable.getIndex()] = value;
         if (value == null)
         	iNrAssigned --;
         else
@@ -142,4 +133,12 @@ public int getIndex() {
     public int nrAssignedVariables() {
         return iNrAssigned;
     }
+    
+    public TimLocation[] toArray() {
+    	return iAssignment;
+    }
+
+	public Assignment<TimEvent, TimLocation> getParentAssignment() {
+		return iParent;
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/tim/model/TimEvent.java b/src/net/sf/cpsolver/itc/tim/model/TimEvent.java
index 8460668..2d50d47 100644
--- a/src/net/sf/cpsolver/itc/tim/model/TimEvent.java
+++ b/src/net/sf/cpsolver/itc/tim/model/TimEvent.java
@@ -7,13 +7,13 @@
 import java.util.Set;
 
 import org.apache.log4j.Logger;
-
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.AssignmentComparable;
+import org.cpsolver.ifs.model.LazySwap;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.model.Variable;
 import org.cpsolver.ifs.util.ToolBox;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazySwap;
+
 import net.sf.cpsolver.itc.heuristics.neighbour.ItcSwap.Swapable;
 
 /**
@@ -270,7 +270,7 @@ public Neighbour<TimEvent, TimLocation> findSwap(Assignment<TimEvent, TimLocatio
         if (r2.isEmpty() && !((TTComp02Model)e1.getModel()).isAllowNoRoom()) return null;
         TimLocation nl1 = new TimLocation(e1, l2.time(), (TimRoom)ToolBox.random(r1));
         TimLocation nl2 = new TimLocation(e2, l1.time(), (TimRoom)ToolBox.random(r2));
-        return new ItcLazySwap<TimEvent, TimLocation>(assignment, nl1, nl2); 
+        return new LazySwap<TimEvent, TimLocation>(nl1, nl2); 
     }
     
     /** Minimal possible starting time (first available slot combined with min start time of all predecessors) */
diff --git a/src/net/sf/cpsolver/itc/tim/model/TimInheritedAssignment.java b/src/net/sf/cpsolver/itc/tim/model/TimInheritedAssignment.java
new file mode 100644
index 0000000..1c64d9f
--- /dev/null
+++ b/src/net/sf/cpsolver/itc/tim/model/TimInheritedAssignment.java
@@ -0,0 +1,56 @@
+package net.sf.cpsolver.itc.tim.model;
+
+import java.util.Arrays;
+import java.util.concurrent.locks.Lock;
+
+import org.cpsolver.ifs.assignment.InheritedAssignment;
+import org.cpsolver.ifs.assignment.context.InheritedAssignmentContextHolder;
+import org.cpsolver.ifs.solution.Solution;
+
+/**
+ * Post Enrollment based Course Timetabling (tim) inherited assignment model.
+ * 
+ * @version
+ * ITC2007 1.0<br>
+ * Copyright (C) 2014 Tomas Muller<br>
+ * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
+ * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
+ * <br>
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ * <br><br>
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * <br><br>
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not see
+ * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
+ */
+public class TimInheritedAssignment extends TimAssignment implements InheritedAssignment<TimEvent, TimLocation> {
+	private long iVersion = -1;
+
+	public TimInheritedAssignment(Solution<TimEvent, TimLocation> solution, int index) {
+		super(new InheritedAssignmentContextHolder<TimEvent, TimLocation>(index, solution.getIteration()));
+		iIndex = index;
+		iVersion = solution.getIteration();
+		iModel = (TimModel) solution.getModel();
+		iParent = (TimAssignment) solution.getAssignment();
+		Lock lock = solution.getLock().readLock();
+		lock.lock();
+		try {
+			iNrAssigned = iParent.nrAssignedVariables();
+			iAssignment = Arrays.copyOf(((TimAssignment)iParent).toArray(), iModel.variables().size());
+		} finally {
+			lock.unlock();
+		}
+	}
+	
+	@Override
+	public long getVersion() {
+		return iVersion;
+	}
+}
diff --git a/src/net/sf/cpsolver/itc/tim/model/TimModel.java b/src/net/sf/cpsolver/itc/tim/model/TimModel.java
index 782c619..a07c93c 100644
--- a/src/net/sf/cpsolver/itc/tim/model/TimModel.java
+++ b/src/net/sf/cpsolver/itc/tim/model/TimModel.java
@@ -382,6 +382,12 @@ public class TimContext extends TTComp02Context {
     	public TimContext(Assignment<TimEvent, TimLocation> assignment) {
     		super(assignment);
     	}
+    	
+    	public TimContext(Assignment<TimEvent, TimLocation> assignment, TimContext parent) {
+            super(assignment, parent);
+            iPrecedenceViolations = parent.iPrecedenceViolations;
+            iNoRoomViolations = parent.iNoRoomViolations;
+    	}
 
         /**
          * Update counters on assignment of an event
@@ -421,4 +427,9 @@ public int noRoomViolations() {
 	public AssignmentConstraintContext<TimEvent, TimLocation> createAssignmentContext(Assignment<TimEvent, TimLocation> assignment) {
 		return new TimContext(assignment);
 	}
+	
+	@Override
+	public TTComp02Context inheritAssignmentContext(Assignment<TimEvent, TimLocation> assignment, TTComp02Context parentContext) {
+        return new TimContext(assignment, (TimContext)parentContext);
+	}
 }
\ No newline at end of file
diff --git a/src/net/sf/cpsolver/itc/tim/model/TimRoom.java b/src/net/sf/cpsolver/itc/tim/model/TimRoom.java
index 9fa2d4f..60872c9 100644
--- a/src/net/sf/cpsolver/itc/tim/model/TimRoom.java
+++ b/src/net/sf/cpsolver/itc/tim/model/TimRoom.java
@@ -1,10 +1,12 @@
 package net.sf.cpsolver.itc.tim.model;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.assignment.context.ConstraintWithContext;
 import org.cpsolver.ifs.model.ConstraintListener;
 
@@ -35,7 +37,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class TimRoom extends ConstraintWithContext<TimEvent, TimLocation, TimRoom.Context> {
+public class TimRoom extends ConstraintWithContext<TimEvent, TimLocation, TimRoom.Context> implements CanInheritContext<TimEvent, TimLocation, TimRoom.Context> {
 	private int iSize;
 	
 	/**
@@ -129,6 +131,10 @@ public Context(Assignment<TimEvent, TimLocation> assignment) {
             		iTable[location.time()] = location;
             }
     	}
+    	
+    	public Context(Assignment<TimEvent, TimLocation> assignment, Context parent) {
+    		iTable = Arrays.copyOf(parent.iTable, 45);
+    	}
 
 		@Override
 		public void assigned(Assignment<TimEvent, TimLocation> assignment, TimLocation location) {
@@ -151,4 +157,9 @@ public TimLocation getLocation(int time) {
 	public Context createAssignmentContext(Assignment<TimEvent, TimLocation> assignment) {
 		return new Context(assignment);
 	}
+
+	@Override
+	public Context inheritAssignmentContext(Assignment<TimEvent, TimLocation> assignment, Context parentContext) {
+		return new Context(assignment, parentContext);
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/tim/model/TimStudent.java b/src/net/sf/cpsolver/itc/tim/model/TimStudent.java
index 98990ed..b032a14 100644
--- a/src/net/sf/cpsolver/itc/tim/model/TimStudent.java
+++ b/src/net/sf/cpsolver/itc/tim/model/TimStudent.java
@@ -1,10 +1,12 @@
 package net.sf.cpsolver.itc.tim.model;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.assignment.context.AssignmentConstraintContext;
+import org.cpsolver.ifs.assignment.context.CanInheritContext;
 import org.cpsolver.ifs.assignment.context.ConstraintWithContext;
 import org.cpsolver.ifs.model.Constraint;
 import org.cpsolver.ifs.model.ConstraintListener;
@@ -34,7 +36,7 @@
  * License along with this library; if not see
  * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
  */
-public class TimStudent extends ConstraintWithContext<TimEvent, TimLocation, TimStudent.Context> {
+public class TimStudent extends ConstraintWithContext<TimEvent, TimLocation, TimStudent.Context> implements CanInheritContext<TimEvent, TimLocation, TimStudent.Context> {
 
 	/**
      * Constructor
@@ -132,6 +134,10 @@ public Context(Assignment<TimEvent, TimLocation> assignment) {
             		iTable[location.time()] = location;
             }
     	}
+    	
+    	public Context(Assignment<TimEvent, TimLocation> assignment, Context parent) {
+    		iTable = Arrays.copyOf(parent.iTable, 45);
+    	}
 
 		@Override
 		public void assigned(Assignment<TimEvent, TimLocation> assignment, TimLocation location) {
@@ -185,4 +191,9 @@ public int score(boolean oneDay, boolean lastTime, boolean threeMore) {
 	public Context createAssignmentContext(Assignment<TimEvent, TimLocation> assignment) {
 		return new Context(assignment);
 	}
+
+	@Override
+	public Context inheritAssignmentContext(Assignment<TimEvent, TimLocation> assignment, Context parentContext) {
+		return new Context(assignment, parentContext);
+	}
 }
diff --git a/src/net/sf/cpsolver/itc/tim/neighbours/TimSwapMove.java b/src/net/sf/cpsolver/itc/tim/neighbours/TimSwapMove.java
index 7061d44..34decc1 100644
--- a/src/net/sf/cpsolver/itc/tim/neighbours/TimSwapMove.java
+++ b/src/net/sf/cpsolver/itc/tim/neighbours/TimSwapMove.java
@@ -2,12 +2,13 @@
 
 import org.cpsolver.ifs.assignment.Assignment;
 import org.cpsolver.ifs.heuristics.NeighbourSelection;
+import org.cpsolver.ifs.model.LazySwap;
 import org.cpsolver.ifs.model.Neighbour;
 import org.cpsolver.ifs.solution.Solution;
 import org.cpsolver.ifs.solver.Solver;
 import org.cpsolver.ifs.util.DataProperties;
 import org.cpsolver.ifs.util.ToolBox;
-import net.sf.cpsolver.itc.heuristics.neighbour.ItcLazySwap;
+
 import net.sf.cpsolver.itc.heuristics.neighbour.ItcSimpleNeighbour;
 import net.sf.cpsolver.itc.heuristics.search.ItcHillClimber.HillClimberSelection;
 import net.sf.cpsolver.itc.tim.model.TTComp02Model;
@@ -92,7 +93,7 @@ public Neighbour<TimEvent, TimLocation> selectNeighbour(Solution<TimEvent, TimLo
                         TimLocation conf = student.getLocation(assignment, location.time());
                         if (conf!=null && !conf.variable().equals(confEvt)) return null;
                     }
-                    return new ItcLazySwap<TimEvent, TimLocation>(assignment,
+                    return new LazySwap<TimEvent, TimLocation>(
                             new TimLocation(event, time, room),
                             new TimLocation(confEvt, location.time(), location.room()));
                 }
diff --git a/src/tim.properties b/src/tim.properties
index 73b9a6f..9b7d5d8 100644
--- a/src/tim.properties
+++ b/src/tim.properties
@@ -49,4 +49,7 @@ Oscillation.UpdateInterval=5000
 Oscillation.WeightMax=5000
 
 #Other
-General.SaveBestUnassigned=0
\ No newline at end of file
+General.SaveBestUnassigned=0
+
+ParallelSolver.SingleSolution=false
+ParallelSolver.SingleSolutionNeighbourCheck=true
\ No newline at end of file
diff --git a/src/ttcomp02.properties b/src/ttcomp02.properties
index 3f9b9ad..9a80185 100644
--- a/src/ttcomp02.properties
+++ b/src/ttcomp02.properties
@@ -45,4 +45,7 @@ SimulatedAnnealing.ReheatLengthCoef=7
 Extensions.Classes=org.cpsolver.ifs.extension.ConflictStatistics
 
 #Other
-General.SaveBestUnassigned=0
\ No newline at end of file
+General.SaveBestUnassigned=0
+
+ParallelSolver.SingleSolution=false
+ParallelSolver.SingleSolutionNeighbourCheck=true
\ No newline at end of file