anchor.diff:  import 'package:sky/animation/animated_value.dart';
   import 'package:sky/animation/animation_performance.dart';
   import 'package:sky/animation/curves.dart';
  +import 'package:sky/animation/forces.dart';
   import 'package:sky/widgets/animated_component.dart';
   import 'package:sky/widgets/basic.dart';
   import 'package:sky/widgets/focus.dart';
  
positive.code:     this.interactive
    }): super(key: key);
    Widget content;
    TransitionDirection direction;
    bool interactive;
    Function onDismissed;
    Function onCompleted;
  
negative.code:       Transition transition = new Transition(
          key: new Key.fromObjectIdentity(historyEntry),
          content: content,
          direction: (i <= state.historyIndex) ? Direction.forward : Direction.reverse,
          interactive: (i == state.historyIndex),
          onDismissed: () {
            setState(() {
  