anchor.diff:    void forEach(void f(E element));
   
     List<E> toList();
  -
  -  /*=R*/ fold/*<R>*/(/*=R*/ initialValue,
  -      /*=R*/ combine(/*=R*/ previousValue, E element)) => null;
   }
   
   class List<E> implements Iterable<E> {
  
positive.code:   int get length;
    Iterable<V> get values;
  }
  
  external bool identical(Object a, Object b);
  
  
negative.code: import 'dart:async';
  
  class Object {
    const Object();
    bool operator ==(other) => identical(this, other);
    String toString() => 'a string';
    int get hashCode => 0;
  