anchor.diff:  }
   
   /// A cubic polynomial mapping of the unit interval.
  -class Cubic implements Curve {
  +class Cubic extends Curve {
     const Cubic(this.a, this.b, this.c, this.d);
   
     final double a;
  
positive.code: }
  
  /// An oscillating curve that shrink in magnitude.
  class BounceOutCurve implements Curve {
    const BounceOutCurve();
    double transform(double t) {
      return _bounce(t);
  
negative.code: }
  
  /// An oscillating curve that first grows and then shrink in magnitude.
  class BounceInOutCurve extends Curve {
    const BounceInOutCurve();
    double transform(double t) {
      if (t < 0.5)
  