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