+std::ostream& operator<<(std::ostream& os, const Board& board);
+
+struct Step {
+ Step(Board board, std::shared_ptr<Step> prev);
+ ~Step();
+
+ Board board;
+ std::shared_ptr<Step> prev;
+
+ std::vector<std::shared_ptr<Step>> successors(std::shared_ptr<Step> shared_this) const;
+ int length() const;
+ int cost(const InvertedBoard& invgoal) const;
+
+ static signed char adjacent[BOARD_SIZE][5];
+ static int count;
+};
+std::ostream& operator<<(std::ostream& os, const Step& step);