diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt b/reactor/Core/src/jetbrains/mps/logic/reactor/core/Controller.kt
similarity index 94%
rename from reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt
rename to reactor/Core/src/jetbrains/mps/logic/reactor/core/Controller.kt
index 8b40f77f..f007a1eb 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/core/Handler.kt
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/core/Controller.kt
@@ -22,21 +22,21 @@ import java.util.*
 
 class FrameStack : LogicalObserver {
 
-    lateinit var current: HandlerFrame
+    lateinit var current: Frame
 
     val observing = HashSet<IdWrapper<Logical<*>>>()
 
     constructor() {
-        this.current = HandlerFrame(this)
+        this.current = Frame(this)
     }
 
-    fun push(): HandlerFrame {
-        val frame = HandlerFrame(this, current)
+    fun push(): Frame {
+        val frame = Frame(this, current)
         this.current = frame
         return frame
     }
 
-    fun reset(frame: HandlerFrame): Unit {
+    fun reset(frame: Frame): Unit {
         this.current = frame
     }
 
@@ -64,7 +64,7 @@ class FrameStack : LogicalObserver {
 
 interface StoreHolder {
 
-    fun store(): OccurrenceStore
+    fun store(): Store
 
     fun addObserver(logical: Logical<*>, obs: (StoreHolder) -> LogicalObserver)
 
@@ -72,21 +72,21 @@ interface StoreHolder {
 }
 
 
-class HandlerFrame : LogicalObserver, StoreHolder
+class Frame : LogicalObserver, StoreHolder
 {
-    val prev: HandlerFrame?
+    val prev: Frame?
 
-    val store: OccurrenceStore
+    val store: Store
 
     private var stack: FrameStack
 
     private lateinit var observers: PersMap<IdWrapper<Logical<*>>, ConsList<(StoreHolder) -> LogicalObserver>>
 
-    constructor(stack: FrameStack, prev: HandlerFrame? = null) {
+    constructor(stack: FrameStack, prev: Frame? = null) {
         this.stack = stack
         this.prev = prev
         this.observers = prev?.observers ?: Maps.of()
-        this.store = OccurrenceStore(prev?.store ?: OccurrenceStore { stack.current }, { stack.current })
+        this.store = Store(prev?.store ?: Store { stack.current }, { stack.current })
     }
 
     override fun store() = store
@@ -129,7 +129,7 @@ class HandlerFrame : LogicalObserver, StoreHolder
 }
 
 
-class Handler {
+class Controller {
 
     private val frameStack = FrameStack()
 
@@ -166,7 +166,7 @@ class Handler {
     fun occurrences(symbol: ConstraintSymbol): Set<ConstraintOccurrence> =
         frameStack.current.store.allOccurrences().filter { co -> co.constraint().symbol() == symbol }.toSet()
 
-    fun tell(constraint: Constraint) {
+    fun activate(constraint: Constraint) {
         try {
             queue(constraint.occurrence({ frameStack.current }, noLogicalContext))
         }
diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/core/MemEvaluationSession.kt b/reactor/Core/src/jetbrains/mps/logic/reactor/core/MemEvaluationSession.kt
index 782f30ab..a081860c 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/core/MemEvaluationSession.kt
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/core/MemEvaluationSession.kt
@@ -17,7 +17,7 @@ import java.util.*
 
 interface SessionObjects {
 
-    fun handler(): Handler
+    fun handler(): Controller
 
 }
 
@@ -80,7 +80,7 @@ class MemEvaluationSession : EvaluationSession, SessionObjects {
     val sessionSolver: SessionSolver
     val trace: EvaluationTrace
 
-    lateinit var handler: Handler
+    lateinit var controller: Controller
 
     private constructor(program: Program, sessionSolver: SessionSolver, trace: EvaluationTrace): super() {
         this.program = program
@@ -89,22 +89,22 @@ class MemEvaluationSession : EvaluationSession, SessionObjects {
     }
 
     fun launch(main: Constraint, profiler: Profiler?) {
-        this.handler = Handler(program.rules(), trace, profiler)
-        handler.tell(main)
+        this.controller = Controller(program.rules(), trace, profiler)
+        controller.activate(main)
     }
 
-    override fun handler() = handler
+    override fun handler() = controller
 
     override fun sessionSolver(): SessionSolver = sessionSolver
 
     override fun constraintSymbols(): Iterable<ConstraintSymbol> =
-        handler.constraintSymbols()
+        controller.constraintSymbols()
 
     override fun constraintOccurrences(): Iterable<ConstraintOccurrence> =
-        handler.allOccurrences()
+        controller.allOccurrences()
 
     override fun constraintOccurrences(symbol: ConstraintSymbol): Iterable<ConstraintOccurrence> =
-        handler.occurrences(symbol)
+        controller.occurrences(symbol)
 
     private class Backend : EvaluationSession.Backend {
 
diff --git a/reactor/Core/src/jetbrains/mps/logic/reactor/core/OccurrenceStore.kt b/reactor/Core/src/jetbrains/mps/logic/reactor/core/Store.kt
similarity index 94%
rename from reactor/Core/src/jetbrains/mps/logic/reactor/core/OccurrenceStore.kt
rename to reactor/Core/src/jetbrains/mps/logic/reactor/core/Store.kt
index b27a9d4a..c1aadc6c 100644
--- a/reactor/Core/src/jetbrains/mps/logic/reactor/core/OccurrenceStore.kt
+++ b/reactor/Core/src/jetbrains/mps/logic/reactor/core/Store.kt
@@ -21,8 +21,8 @@ import com.github.andrewoma.dexx.collection.Vector as PersVector
  * @author Fedor Isakov
  */
 
-fun Constraint.occurrence(currentFrame: () -> HandlerFrame, context: LogicalContext): ConstraintOccurrence =
-    MemConstraintOccurrence(currentFrame, this, occurrenceArguments(context))
+fun Constraint.occurrence(currentFrame: () -> Frame, context: LogicalContext): ConstraintOccurrence =
+    Occurrence(currentFrame, this, occurrenceArguments(context))
 
 fun ConstraintOccurrence.isStored(): Boolean =
     // TODO: superfluous cast
@@ -55,7 +55,7 @@ interface OccurrenceIndex {
 /**
  * TODO: make this class persistent.
  */
-class OccurrenceStore : LogicalObserver, OccurrenceIndex {
+class Store : LogicalObserver, OccurrenceIndex {
 
     val currentFrame: () -> StoreHolder
 
@@ -67,7 +67,7 @@ class OccurrenceStore : LogicalObserver, OccurrenceIndex {
 
     var value2occurrences: PersMap<Any, IdHashSet<ConstraintOccurrence>>
 
-    constructor(copyFrom: OccurrenceStore, currentFrame: () -> StoreHolder)
+    constructor(copyFrom: Store, currentFrame: () -> StoreHolder)
     {
         this.currentFrame = currentFrame
         this.symbol2occurrences = copyFrom.symbol2occurrences
@@ -255,7 +255,7 @@ class OccurrenceStore : LogicalObserver, OccurrenceIndex {
 
 
 
-private data class MemConstraintOccurrence(val currentFrame: () -> HandlerFrame, val constraint: Constraint, val arguments: List<*>) :
+private data class Occurrence(val currentFrame: () -> Frame, val constraint: Constraint, val arguments: List<*>) :
     ConstraintOccurrence,
     LogicalObserver,
     StoreItem
@@ -265,7 +265,7 @@ private data class MemConstraintOccurrence(val currentFrame: () -> HandlerFrame,
 
     override var stored = false
 
-    constructor(currentFrame: () -> HandlerFrame, constraint: Constraint, arguments: Collection<*>) :
+    constructor(currentFrame: () -> Frame, constraint: Constraint, arguments: Collection<*>) :
         this(currentFrame, constraint, ArrayList(arguments))
     {
         for (a in arguments) {
diff --git a/reactor/Test/test/TestHandler.kt b/reactor/Test/test/TestController.kt
similarity index 98%
rename from reactor/Test/test/TestHandler.kt
rename to reactor/Test/test/TestController.kt
index 782ba895..d793ba40 100644
--- a/reactor/Test/test/TestHandler.kt
+++ b/reactor/Test/test/TestController.kt
@@ -1,4 +1,4 @@
-import jetbrains.mps.logic.reactor.core.Handler
+import jetbrains.mps.logic.reactor.core.Controller
 import jetbrains.mps.logic.reactor.core.SessionObjects
 import jetbrains.mps.logic.reactor.evaluation.ConstraintOccurrence
 import jetbrains.mps.logic.reactor.evaluation.EvaluationFailureException
@@ -19,7 +19,7 @@ import solver.MemSessionSolver
  */
 
 
-class TestHandler {
+class TestController {
 
     @Before fun beforeTest() {
     }
@@ -29,8 +29,8 @@ class TestHandler {
     }
 
     private class MockSession(val solver: SessionSolver) : EvaluationSession(), SessionObjects {
-        lateinit var handler: Handler
-        override fun handler(): Handler = handler
+        lateinit var controller: Controller
+        override fun handler(): Controller = controller
         override fun sessionSolver(): SessionSolver = solver
         override fun constraintSymbols(): MutableIterable<ConstraintSymbol> = TODO()
         override fun constraintOccurrences(): MutableIterable<ConstraintOccurrence> = TODO()
@@ -59,10 +59,10 @@ class TestHandler {
         MemSessionSolver(expressionSolver, equalsSolver).apply {
             init(PredicateSymbol("equals", 2), JavaPredicateSymbol.EXPRESSION0, JavaPredicateSymbol.EXPRESSION1, JavaPredicateSymbol.EXPRESSION2, JavaPredicateSymbol.EXPRESSION3) }
 
-    private fun Builder.handler(vararg occurrences: ConstraintOccurrence): Handler {
+    private fun Builder.handler(vararg occurrences: ConstraintOccurrence): Controller {
         MockSession.init(sessionSolver(env.expressionSolver, env.equalsSolver))
-        val handler = Handler(rules, occurrences = listOf(* occurrences))
-        MockSession.ourBackend.session.handler = handler
+        val handler = Controller(rules, occurrences = listOf(* occurrences))
+        MockSession.ourBackend.session.controller = handler
         return handler
     }
 
diff --git a/reactor/Test/test/TestOccurrenceStore.kt b/reactor/Test/test/TestOccurrenceStore.kt
index fede711a..eed90357 100644
--- a/reactor/Test/test/TestOccurrenceStore.kt
+++ b/reactor/Test/test/TestOccurrenceStore.kt
@@ -14,11 +14,11 @@ import org.junit.Before
 
 class TestOccurrenceStore {
 
-    class MockProxy(val _store: () -> OccurrenceStore) : LogicalObserver, StoreHolder {
+    class MockProxy(val _store: () -> Store) : LogicalObserver, StoreHolder {
 
         private var observerList = emptyConsList<Pair<Logical<*>, LogicalObserver>>()
 
-        override fun store(): OccurrenceStore = _store()
+        override fun store(): Store = _store()
 
         override fun addObserver(logical: Logical<*>, obs: (StoreHolder) -> LogicalObserver)  {
             if (!observerList.any { obs -> obs.first === logical }) {               // referential equality!
@@ -46,11 +46,11 @@ class TestOccurrenceStore {
         }
     }
 
-    lateinit var occstore: OccurrenceStore
+    lateinit var occstore: Store
 
     @Before
     fun setup() {
-        occstore = OccurrenceStore { MockProxy {  occstore } }
+        occstore = Store { MockProxy {  occstore } }
     }
 
     @Test