anchor.diff:    }
   
     @override
  -  Set<E> union(Set<E> other) => new Set<E>.from(this)..addAll(other);
  -
  -  @override
  -  Setlet<E> intersection(Set<Object> other) =>
  -      new Setlet<E>.from(this.where((e) => other.contains(e)));
  -
  -  @override
  -  Setlet<E> difference(Set<Object> other) =>
  -      new Setlet<E>.from(this.where((e) => !other.contains(e)));
  +  Set<E> union(Set<E> other) => Set<E>.from(this)..addAll(other);
  +
  +  @override
  +  Setlet<E> intersection(Set<Object?> other) =>
  +      Setlet<E>.from(this.where((e) => other.contains(e)));
  +
  +  @override
  +  Setlet<E> difference(Set<Object?> other) =>
  +      Setlet<E>.from(this.where((e) => !other.contains(e)));
   
     @override
     Setlet<E> toSet() {
  -    Setlet<E> result = new Setlet<E>();
  +    Setlet<E> result = Setlet<E>();
       if (_extra == null) {
         result._contents = _contents;
       } else if (_extra == _MARKER) {
  
positive.code:   }
  
    @override
    bool containsAll(Iterable<Object> other) {
      for (E e in other) {
        if (!this.contains(e)) return false;
      }
      return true;
  
negative.code:   }
  
    @override
    void removeAll(Iterable<Object?> other) {
      other.forEach(remove);
    }
  
  