anchor.diff:    Map<int, TapGesture> _gestureMap = new Map<int, TapGesture>();
   
     void addPointer(PointerInputEvent event) {
  +    assert(!_gestureMap.containsKey(event.pointer));
       _gestureMap[event.pointer] = new TapGesture(
         gestureRecognizer: this,
         event: event
  
positive.code:   }
  
    void cancel() {
      // If we won the arena already, then _entry is resolved, so resolving
      // again is a no-op. But we still need to clean up our own state.
      if (_wonArena)
        reject();
  
negative.code:   }
  
    void acceptGesture(int pointer) {
      assert(_gestureMap.containsKey(pointer));
      _gestureMap[pointer]?.accept();
    }
  
    void rejectGesture(int pointer) {
      assert(_gestureMap.containsKey(pointer));
      _gestureMap[pointer]?.reject();
    }
  
  