diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/evaluation/MatchRule.java b/reactor/Core/src/jetbrains/mps/logic/reactor/evaluation/MatchRule.java
index 7ebb1850..6a873867 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/evaluation/MatchRule.java
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/evaluation/MatchRule.java
@@ -23,6 +23,8 @@ import jetbrains.mps.logic.reactor.program.Rule;
 /**
  * A binding of a rule and the constraint occurrences that matched its head.
  *
+ * // FIXME rename to RuleMatch
+ *
  * @author Fedor Isakov
  */
 public interface MatchRule {
diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/program/Handler.java b/reactor/Core/src/jetbrains/mps/logic/reactor/program/Handler.java
index f2a277f9..625fef21 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/program/Handler.java
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/program/Handler.java
@@ -19,6 +19,7 @@ package jetbrains.mps.logic.reactor.program;
 /**
  * A handler is a container of rules.
  * <p>
+ * FIXME to be renamed to RulesList
  * @author Fedor Isakov
  */
 public abstract class Handler {
diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/program/Program.java b/reactor/Core/src/jetbrains/mps/logic/reactor/program/Program.java
index ca571379..943a51da 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/program/Program.java
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/program/Program.java
@@ -25,30 +25,36 @@ import java.util.List;
 /**
  * A collection of handlers that constitute a constraint rules program.
  *
+ * FIXME a handler is to be renamed to RulesList
  * @author Fedor Isakov
  */
 public abstract class Program {
 
     public abstract String name();
 
-    public abstract Iterable<ConstraintSymbol> constraintSymbols();
+    /**
+     * @deprecated no usages
+     * @return
+     */
+    @Deprecated
+    public Iterable<ConstraintSymbol> constraintSymbols() { throw new UnsupportedOperationException (); }
 
-    public abstract List<Class<?>> constraintArgumentTypes(ConstraintSymbol constraintSymbol);
+    /**
+     * @deprecated no usages
+     * @return
+     */
+    @Deprecated
+    public List<Class<?>> constraintArgumentTypes(ConstraintSymbol constraintSymbol) { throw new UnsupportedOperationException (); }
 
-    public abstract Iterable<PredicateSymbol> predicateSymbols();
+    /**
+     * @deprecated no usages
+     * @return
+     */
+    @Deprecated
+    public Iterable<PredicateSymbol> predicateSymbols() { throw new UnsupportedOperationException (); }
 
     public abstract Iterable<Handler> handlers();
 
-    /**
-     * @deprecated use the overloaded method with InvocationContext parameter
-     */
-    @Deprecated
-    public List<?> instantiateArguments(List<?> arguments, LogicalContext logicalContext) {
-        throw new UnsupportedOperationException();
-    }
-
-    public List<?> instantiateArguments(List<?> arguments, LogicalContext logicalContext, InvocationContext ignore) {
-        return instantiateArguments(arguments, logicalContext);
-    }
+    public abstract List<?> instantiateArguments(List<?> arguments, LogicalContext logicalContext, InvocationContext invocationContext);
 
 }
diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/program/Rule.java b/reactor/Core/src/jetbrains/mps/logic/reactor/program/Rule.java
index dda9379b..25e4b79f 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/program/Rule.java
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/program/Rule.java
@@ -26,8 +26,16 @@ public abstract class Rule {
 
     public abstract Rule.Kind kind();
 
+    /**
+     * A tag uniquely identifies the rule.
+     */
     public abstract String tag();
 
+    /**
+     * An origin serves as justification for all constraints affected by this rule.
+     */
+    public Object origin() { return null; }
+
     public abstract Iterable<Constraint> headKept();
 
     public abstract Iterable<Constraint> headReplaced();
diff --git a/reactor/Test/src/program/MockProgram.kt b/reactor/Test/src/program/MockProgram.kt
index 266c3780..8c4c7418 100644
--- a/reactor/Test/src/program/MockProgram.kt
+++ b/reactor/Test/src/program/MockProgram.kt
@@ -2,6 +2,7 @@
  * @author Fedor Isakov
  */
 
+import jetbrains.mps.logic.reactor.evaluation.InvocationContext
 import jetbrains.mps.logic.reactor.logical.LogicalContext
 import jetbrains.mps.logic.reactor.logical.MetaLogical
 import jetbrains.mps.logic.reactor.program.*
@@ -96,6 +97,7 @@ class MockProgram(val name: String, val handlers: List<Handler>, val registry: M
 
     override fun name(): String = name
 
+
     override fun constraintSymbols(): Iterable<ConstraintSymbol> =
         registry.constraintSymbols()
 
@@ -105,7 +107,7 @@ class MockProgram(val name: String, val handlers: List<Handler>, val registry: M
     override fun predicateSymbols(): Iterable<PredicateSymbol> =
         registry.predicateSymbols()
 
-    override fun instantiateArguments(arguments: List<*>, logicalContext: LogicalContext): List<*> =
+    override fun instantiateArguments(arguments: List<*>, logicalContext: LogicalContext, invocationContext: InvocationContext): List<*> =
         arguments.map { a ->
             if (a is MetaLogical<*>) logicalContext.variable(a)
             else a