anchor.diff:      if ((_bitmap & mask) != 0) {
         int index = _popcount(_bitmap & (mask - 1));
         _Node<K, V> m = _array[index];
  -      return m._intersectWith(owner, keyValues, kvLength, combine, hash, depth + 1);
  +      return m._intersectWith(owner, pairs, pairsLength, combine, hash, depth + 1);
       } else {
         return new _EmptyMap(owner);
       }
  
positive.code:   int _hash;
    LinkedList<Pair<K, V>> _pairs;
  
    _Leaf.abc(_Owner owner, this._hash, pairs, int kvLength) : super(owner, kvLength) {
      this._pairs = pairs;
      assert(kvLength == pairs.length);
    }
  
    factory _Leaf.ensureOwner(_Leaf old, _Owner owner, hash, pairs, int length) {
  
negative.code:   _Node(this._owner, this._length);
  
    V _get(K key, int hash, int depth);
    _Node<K, V> _insertWith(_Owner owner, LinkedList<Pair<K, V>> pairs, int pairsLength,
        V combine(V x, V y), int hash, int depth);
    _Node<K, V> _intersectWith(_Owner owner, LinkedList<Pair<K, V>> pairs, int pairsLength,
        V combine(V x, V y), int hash, int depth);
    _Node<K, V> _delete(_Owner owner, K key, int hash, int depth, bool missingOk);
    _Node<K, V> _update(_Owner owner, K key, dynamic updateF, int hash, int depth);
  