diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt b/reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt
index 782f4299..29e3d093 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt
@@ -40,7 +40,7 @@ class Handler {
                     stored.filter { co -> constraint.matches(co) && acceptable(co) }
         }
 
-        val match = matcher.lookupMatches(active).find { pm -> pm.rule.guard().all { prd -> askPredicate(prd) } }
+        val match = matcher.lookupMatches(active).find { pm -> pm.rule.checkGuard(pm.logicalContext()) }
 
         if (match != null) {
             for ((cst, occ) in match.discarded) {
@@ -68,17 +68,14 @@ class Handler {
         }
     }
 
-    private fun askPredicate(predicate: Predicate): Boolean =
-        sessionSolver.ask(predicate.symbol(), * predicate.arguments().toTypedArray())
+    private fun Rule.checkGuard(logicalContext: LogicalContext): Boolean =
+        guard().all { prd -> askPredicate(prd.invocation(logicalContext)) }
+
+    private fun askPredicate(invocation: PredicateInvocation): Boolean =
+        sessionSolver.ask(invocation.predicate().symbol(), * invocation.arguments().toTypedArray())
 
     private fun tellPredicate(invocation: PredicateInvocation) {
         sessionSolver.tell(invocation.predicate().symbol(), * invocation.arguments().toTypedArray())
     }
 
 }
-
-interface HandlingContext {
-
-    fun substitute(logicalPattern: LogicalPattern<*>) : Any
-
-}
\ No newline at end of file
diff --git a/reactor/Test/test/LogicalHelper.kt b/reactor/Test/test/LogicalHelper.kt
index c2029468..215d6e2e 100644
--- a/reactor/Test/test/LogicalHelper.kt
+++ b/reactor/Test/test/LogicalHelper.kt
@@ -30,8 +30,11 @@ inline fun <reified T: Any> logicalPattern(name1: String, name2: String, name3:
 
 fun <T: Any> Logical<T>.get(): T = findRoot().value()
 
-fun <T: Any> TestLogical<T>.set(t: T) {
-    find().value = t
+fun <T: Any> Logical<T>.set(t: T) {
+    if (this is TestLogical<T>)
+        find().value = t
+    else
+        throw IllegalStateException("unexpected receiver $this")
 }
 
 data class TestLogical<T>(val name: String, var value: T?, var parent: TestLogical<T>?) : Logical<T> {
@@ -69,6 +72,8 @@ data class TestLogical<T>(val name: String, var value: T?, var parent: TestLogic
     fun union(other: TestLogical<T>) {
         if (find() != other.find()) find().parent = other
     }
+
+    override fun toString(): String = "$name(^${parent?.name ?: null})=$value"
 }
 
 data class TestLogicalPattern<T>(val name: String, val type: Class<T>) : LogicalPattern<T> {
diff --git a/reactor/Test/test/RulesHelper.kt b/reactor/Test/test/RulesHelper.kt
index 63178c07..eb0679e2 100644
--- a/reactor/Test/test/RulesHelper.kt
+++ b/reactor/Test/test/RulesHelper.kt
@@ -150,6 +150,6 @@ private data class TestConstraintOccurrence(val constraint: Constraint, val argu
 
     override fun arguments(): Collection<Any> = arguments
 
-    override fun toString(): String = "#${constraint().symbol()}(${arguments().joinToString()})#${id}"
+    override fun toString(): String = "${constraint().symbol()}(${arguments().joinToString()})"
 
 }
diff --git a/reactor/Test/test/TestProgram.kt b/reactor/Test/test/TestProgram.kt
index 3b685df6..16a49ffb 100644
--- a/reactor/Test/test/TestProgram.kt
+++ b/reactor/Test/test/TestProgram.kt
@@ -80,10 +80,47 @@ class TestProgram {
             )
         ).session("logicalValue").run {
             assertEquals(setOf(ConstraintSymbol("foo", 1), ConstraintSymbol("bar", 1)), constraintSymbols())
+            assertEquals(2, constraintOccurrences().count())
             val yval = constraintOccurrences(ConstraintSymbol("bar", 1)).first().arguments().first()
             assertEquals(66, (yval as Logical<Int>).get())
         }
     }
 
+    @Test
+    fun simpleProgram() {
+        val (X, Y) = logicalPattern<Int>("X", "Y")
+
+        program(
+            rule("main",
+                headReplaced(
+                    constraint("main")
+                ),
+                body(
+                    statement({ x -> x.set(5) }, X),
+                    constraint("val", X)
+                )
+            ),
+            rule("dec",
+                headReplaced(
+                    constraint("val", X)
+                ),
+                guard(
+                    expression({ x -> x.get() > 0 }, X)
+                ),
+                body(
+                    constraint("trail", X),
+                    statement({ x, y -> y.set(x.get() - 1)}, X, Y),
+                    constraint("val", Y)
+                )
+            )
+        ).session("dec").run {
+            assertEquals(setOf(ConstraintSymbol("val", 1), ConstraintSymbol("trail", 1)), constraintSymbols())
+            assertEquals(1, constraintOccurrences(ConstraintSymbol.symbol("val", 1)).count())
+            val a = constraintOccurrences(ConstraintSymbol.symbol("val", 1)).first().arguments().first()
+            assertEquals(0, (a as Logical<Int>).get())
+            assertEquals(5, constraintOccurrences(ConstraintSymbol.symbol("trail", 1)).count())
+            println(constraintOccurrences(ConstraintSymbol.symbol("trail", 1)))
+        }
+    }
 
 }