anchor.diff:  
   Iterable zipEntries([Iterable keys, Iterable items]) => $package$zipEntries(keys, items);
   
  -Iterable $package$zipPairs([Iterable firstElements, Iterable secondElements]) => $package$mapPairs(new dart$Callable(([$dart$core.Object first, $dart$core.Object second]) => new Tuple.$withList([first, second], null)), firstElements, secondElements);
  +Iterable $package$zipPairs([Iterable firstElements, Iterable secondElements]) => $package$mapPairs(new dart$Callable(([$dart$core.Object first, $dart$core.Object second]) => new Tuple.$withList([first, second])), firstElements, secondElements);
   
   Iterable zipPairs([Iterable firstElements, Iterable secondElements]) => $package$zipPairs(firstElements, secondElements);
   
  
positive.code:     Empty trimTrailing([Callable trimming]);
      static Empty $trimTrailing([final Empty $this, Callable trimming]) => $this;
      Tuple slice([$dart$core.int index]);
      static Tuple $slice([final Empty $this, $dart$core.int index]) => new Tuple.$withList([$this, $this], null);
      void each([Callable step]);
      static void $each([final Empty $this, Callable step]) {}
  }
  
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)) {
  