anchor.diff:      return new WhereIterable<E>(this, f);
     }
   
  -  Iterable expand(Iterable f(E element)) {
  -    return new ExpandIterable<E, dynamic>(this, f);
  +  Iterable<T> expand<T>(Iterable<T> f(E element)) {
  +    return new ExpandIterable<E, T>(this, f);
     }
   
     void addAll(Iterable<E> collection) {
  
positive.code:     return value;
    }
  
    fold(var initialValue, combine(var previousValue, E element)) {
      var value = initialValue;
      int length = this.length;
      for (int i = 0; i < length; i++) {
  
negative.code:     }
    }
  
    Iterable<T> map<T>(T f(E element)) {
      return new MappedListIterable<E, T>(this, f);
    }
  
    String join([String separator = ""]) {
  