diff --git a/src/App/App.tsx b/src/App/App.tsx
index 9423dd9..3c01e62 100644
--- a/src/App/App.tsx
+++ b/src/App/App.tsx
@@ -126,7 +126,6 @@ export function App() {
         <AST {...ast}/>
         {rt.map((rt, idx) => <><hr/><div className={"runtimeState"+(idx===rtIdx?" active":"")} onClick={() => setRTIdx(idx)}>
           <ShowEnvironment environment={rt.environment}/>
-          <br/>
           <ShowMode mode={rt.mode} statechart={ast}/>
         </div></>)}
       </aside>
@@ -135,15 +134,15 @@ export function App() {
 }
 
 function ShowEnvironment(props: {environment: Environment}) {
-  return <>{[...props.environment.entries()].map(([variable,value]) =>
+  return <div>{[...props.environment.entries()].map(([variable,value]) =>
     `${variable}: ${value}`
-  ).join(', ')}</>;
+  ).join(', ')}</div>;
 }
 
 function ShowMode(props: {mode: Mode, statechart: Statechart}) {
   const activeLeafs = getActiveLeafs(props.mode, props.statechart);
-  return <>{[...activeLeafs].map(uid =>
-    stateDescription(props.statechart.uid2State.get(uid)!)).join(",")}</>;
+  return <div>{[...activeLeafs].map(uid =>
+    stateDescription(props.statechart.uid2State.get(uid)!)).join(",")}</div>;
 }
 
 function getActiveLeafs(mode: Mode, sc: Statechart) {
diff --git a/src/VisualEditor/interpreter.ts b/src/VisualEditor/interpreter.ts
index 9a9ed0d..878bdbb 100644
--- a/src/VisualEditor/interpreter.ts
+++ b/src/VisualEditor/interpreter.ts
@@ -1,18 +1,14 @@
 import { evalExpr } from "./actionlang_interpreter";
 import { computeArena, ConcreteState, getDescendants, isAncestorOf, isOverlapping, OrState, Statechart, stateDescription, Transition } from "./ast";
 import { Action } from "./label_ast";
-import { Environment, RaisedEvents, Mode, RT_Statechart, initialRaised } from "./runtime_types";
+import { Environment, RaisedEvents, Mode, RT_Statechart, initialRaised, BigStep } from "./runtime_types";
 
-export function initialize(ast: Statechart): RT_Statechart {
-  const {enteredStates, environment, ...raised} = enterDefault(ast.root, {
+export function initialize(ast: Statechart): BigStep {
+  let {enteredStates, environment, ...raised} = enterDefault(ast.root, {
     environment: new Map(),
     ...initialRaised,
   });
-  return {
-    mode: enteredStates,
-    environment,
-    ...raised,
-  };
+  return handleInternalEvents(ast, {mode: enteredStates, environment, ...raised});
 }
 
 type ActionScope = {
@@ -168,7 +164,7 @@ export function execAction(action: Action, rt: ActionScope): ActionScope {
   throw new Error("should never reach here");
 }
 
-export function handleEvent(event: string, statechart: Statechart, activeParent: ConcreteState, {environment, mode, ...raised}: RT_Statechart): RT_Statechart {
+export function handleEvent(event: string, statechart: Statechart, activeParent: ConcreteState, {environment, mode, ...raised}: RT_Statechart & RaisedEvents): RT_Statechart & RaisedEvents {
   const arenasFired = new Set<OrState>();
   for (const state of activeParent.children) {
     if (mode.has(state.uid)) {
@@ -208,22 +204,27 @@ export function handleEvent(event: string, statechart: Statechart, activeParent:
   return {environment, mode, ...raised};
 }
 
-export function handleInputEvent(event: string, statechart: Statechart, rt: RT_Statechart): RT_Statechart {
-  let {mode, environment, internalEvents, outputEvents} = handleEvent(event, statechart, statechart.root, rt);
+export function handleInputEvent(event: string, statechart: Statechart, {mode, environment}: {mode: Mode, environment: Environment}): BigStep {
+  let raised = initialRaised;
 
-  while (internalEvents.length > 0) {
-    const [event, ...rest] = internalEvents;
-    ({mode, environment, internalEvents, outputEvents} = handleEvent(event, statechart, statechart.root, {mode, environment, internalEvents: rest, outputEvents}));
+  ({mode, environment, ...raised} = handleEvent(event, statechart, statechart.root, {mode, environment, ...raised}));
+
+  return handleInternalEvents(statechart, {mode, environment, ...raised});
+}
+
+export function handleInternalEvents(statechart: Statechart, {mode, environment, ...raised}: RT_Statechart & RaisedEvents): BigStep {
+  while (raised.internalEvents.length > 0) {
+    const [internalEvent, ...rest] = raised.internalEvents;
+    ({mode, environment, ...raised} = handleEvent(internalEvent, statechart, statechart.root, {mode, environment, internalEvents: rest, outputEvents: raised.outputEvents}));
   }
-
-  return {mode, environment, internalEvents, outputEvents};
+  return {mode, environment, outputEvents: raised.outputEvents};
 }
 
 function transitionDescription(t: Transition) {
   return stateDescription(t.src) + ' ➔ ' + stateDescription(t.tgt);
 }
 
-export function fireTransition(t: Transition, arena: OrState, srcPath: ConcreteState[], tgtPath: ConcreteState[], {mode, environment, ...raised}: RT_Statechart): RT_Statechart {
+export function fireTransition(t: Transition, arena: OrState, srcPath: ConcreteState[], tgtPath: ConcreteState[], {mode, environment, ...raised}: RT_Statechart & RaisedEvents): RT_Statechart & RaisedEvents {
 
   // console.log('fire ', transitionDescription(t), {arena, srcPath, tgtPath});
 
@@ -233,8 +234,6 @@ export function fireTransition(t: Transition, arena: OrState, srcPath: ConcreteS
   toExit.delete(arena.uid); // do not exit the arena itself
   const exitedMode = mode.difference(toExit);
 
-  // console.log('exitedMode', exitedMode);
-
   // exec transition actions
   for (const action of t.label[0].actions) {
     ({environment, ...raised} = execAction(action, {environment, ...raised}));
@@ -245,7 +244,5 @@ export function fireTransition(t: Transition, arena: OrState, srcPath: ConcreteS
   ({enteredStates, environment, ...raised} = enterPath(tgtPath.slice(1), {environment, ...raised}));
   const enteredMode = exitedMode.union(enteredStates);
 
-  // console.log('enteredMode', enteredMode);
-
   return {mode: enteredMode, environment, ...raised};
 }
diff --git a/src/VisualEditor/runtime_types.ts b/src/VisualEditor/runtime_types.ts
index d665de6..1f1c483 100644
--- a/src/VisualEditor/runtime_types.ts
+++ b/src/VisualEditor/runtime_types.ts
@@ -4,6 +4,10 @@
 // for basic states (= empty AND-states), the modal configuration is just an empty object
 // export type Mode = {[uid:string]: Mode};
 
+import { Transition } from "./ast";
+
+export type Timestamp = number; // milliseconds since begin of simulation
+export type Event = string;
 
 export type Mode = Set<string>; // set of active states
 
@@ -14,7 +18,7 @@ export type RT_Statechart = {
   mode: Mode;
   environment: Environment;
   // history: // TODO
-} & RaisedEvents;
+}
 
 export type BigStep = {
   from: RT_Statechart;
@@ -28,10 +32,9 @@ export type RaisedEvents = {
   outputEvents: string[];
 };
 
+export type Timers = Map<string, number>; // transition uid -> timestamp
+
 export const initialRaised: RaisedEvents = {
   internalEvents: [],
   outputEvents: [],
 }
-
-// export type RT_Events = {
-// };