anchor.diff:  // Tuple.dart
   //
   
  -class Tuple implements List, Sequence, Iterable {
  +class Tuple extends impl$BaseList implements Sequence, Iterable {
     final $dart$core.List _list;
   
     Tuple($dart$core.Object first, Iterable rest) : _list = [] {
  
positive.code:   Iterable follow([$dart$core.Object head])
      =>  withLeading(head);
  
    // bridge methods
    @$dart$core.override
    $dart$core.bool defines([$dart$core.Object index])
      =>  List.$defines(this, index);
  
    @$dart$core.override
    $dart$core.bool get empty
      =>  _list.length == 0;
  
    @$dart$core.override
    get([$dart$core.Object index])
      =>  List.$get(this, index);
  
    @$dart$core.override
    getFromLast([$dart$core.int index])
      =>  List.$getFromLast(this, index);
  
    @$dart$core.override
    Iterator iterator()
      =>  List.$iterator(this);
  
    @$dart$core.override
    $dart$core.int get size
      =>  List.$get$size(this);
  
    @$dart$core.override
    $dart$core.Object get first
      =>  Iterable.$get$first(this);
  
    @$dart$core.override
    Iterable map([Callable collecting])
      =>  Iterable.$map(this, collecting);
  
    @$dart$core.override
    Iterable flatMap([Callable collecting])
      =>  Iterable.$flatMap(this, collecting);
  
    @$dart$core.override
    Iterable get rest
      =>  Iterable.$get$rest(this);
  
    @$dart$core.override
    $dart$core.String toString()
      =>  Iterable.$get$string(this);
  
    @$dart$core.override
    void each([Callable step])
      =>  Iterable.$each(this, step);
  
    @$dart$core.override
    $dart$core.bool contains([$dart$core.Object element])
      =>  Collection.$contains(this, element);
  
    @$dart$core.override
    Sequence sequence()
      =>  Sequence.$sequence(this);
  }
  
  //
  
negative.code:   Iterable follow([$dart$core.Object head])
      =>  new Tuple(head, this);
  
    Sequential sort([Callable c]) {
      var newList = _list.toList();
      newList.sort(c.$delegate$);
      return new ArraySequence(new Array._withList(newList));
    }
  
    @$dart$core.override
    $dart$core.bool get empty
      =>  _list.length == 0;
  }
  
  //
  