class ADS_set<Key,N>::Iterator {
public:
  using value_type = Key;
  using difference_type = std::ptrdiff_t;
  using reference = const value_type &;
  using pointer = const value_type *;
  using iterator_category = std::forward_iterator_tag;

private:
	key_type a , b;
  element *pos;
	bool special{false};
	value_type stop;
  void skip() {
  while (pos->mode != Mode::used && pos->mode != Mode::end) ++pos;
  if (special && pos->mode != Mode::end && std::equal_to<Key>{}(pos->key,stop))
    while (pos->mode != Mode::end) ++pos;
}

public:
	explicit Iterator(element *pos = nullptr): pos{pos} { if (pos) skip(); }
	explicit Iterator(element *pos, const key_type &stop): pos{pos}, special{true}, stop{stop} { if (pos) skip(); }
  reference operator*() const { return pos->key; }
  pointer operator->() const { return &pos->key; }

  Iterator &operator++() { ++pos; skip(); return *this; }

  Iterator operator++(int) { auto rc {*this}; ++*this; return rc; }
  friend bool operator==(const Iterator &lhs, const Iterator &rhs) { return lhs.pos == rhs.pos; }
  friend bool operator!=(const Iterator &lhs, const Iterator &rhs) { return !(lhs == rhs); }
};



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const_iterator x(const key_type &a, const key_type &b) const {
		if (!count(b)) return end();
		const_iterator rc{table, b};
		while (rc != end() && !std::equal_to<Key>{}(*rc, a)) ++rc;
		return rc;
	}