anchor.diff:      Empty by([$dart$core.int step]);
       static Empty $by([final Empty $this, $dart$core.int step]) => $this;
       Tuple withLeading([$dart$core.Object element]);
  -    static Tuple $withLeading([final Empty $this, $dart$core.Object element]) => new Tuple.$withList([element], null);
  +    static Tuple $withLeading([final Empty $this, $dart$core.Object element]) => new Tuple.$withList([element]);
       Tuple withTrailing([$dart$core.Object element]);
  -    static Tuple $withTrailing([final Empty $this, $dart$core.Object element]) => new Tuple.$withList([element], null);
  +    static Tuple $withTrailing([final Empty $this, $dart$core.Object element]) => new Tuple.$withList([element]);
       Sequential append([Sequential elements]);
       static Sequential $append([final Empty $this, Sequential elements]) => elements;
       Sequential prepend([Sequential elements]);
  
positive.code:     Sequential trimTrailing([Callable trimming]);
      static Sequential $trimTrailing([final Sequential $this, Callable trimming]) => List.$trimTrailing($this, trimming).sequence();
      Tuple slice([$dart$core.int index]);
      static Tuple $slice([final Sequential $this, $dart$core.int index]) => new Tuple.$withList([$this.spanTo(Integer.instance(index - 1)) as Sequential, $this.spanFrom(Integer.instance(index)) as Sequential], null);
      Tuple withLeading([$dart$core.Object element]);
      Sequence withTrailing([$dart$core.Object element]);
      Sequential append([Sequential elements]);
  
negative.code:     Entry([$dart$core.Object this.key, $dart$core.Object this.item]) {}
      $dart$core.Object key;
      $dart$core.Object item;
      Tuple get pair => new Tuple.$withList([key, item]);
      Entry get coalesced => (() {
          $dart$core.bool doElse$0 = true;
          if (!(item == null)) {
  