1 files changed, 6 insertions, 4 deletions
diff --git a/src/jrummikub/ai/fdsolver/Constraint.java b/src/jrummikub/ai/fdsolver/Constraint.java
index f7955ce..b081d4b 100644
--- a/src/jrummikub/ai/fdsolver/Constraint.java
+++ b/src/jrummikub/ai/fdsolver/Constraint.java
@@ -2,10 +2,12 @@ package jrummikub.ai.fdsolver;
 
 import java.util.Collection;
 
-public interface Constraint {
-	public Collection<Var<?>> getWatchedVars();
+public abstract class Constraint {
+	Collection<Propagator> cachedPropagators;
+	
+	public abstract Collection<Var<?>> getWatchedVars();
 
-	public Collection<Propagator> getPropagators(boolean negate);
+	public abstract Collection<Propagator> getPropagators(boolean negate);
 
-	public Satisfiability getSatisfiability();
+	public abstract Satisfiability getSatisfiability();
 }