anchor.diff:      _sorted.add(element);
     }
   
  -
  +  @override
     bool remove(Object element) => _sorted.remove(element);
   }
  
positive.code: 
    E operator[](int index) => _sorted[index];
  
    void clear() => _sorted.clear();
  
    void addAll(Iterable<E> elements) {
      for(var e in elements) {
        this.add(e);
  
negative.code:   }
  
    // TODO: binary insert? O(ln) is better than O(n)
    @override
    void add(E element) {
      for(int i = 0; i < _sorted.length; i++) {
        var compare = element.compareTo(_sorted[i]);
  