156. cannon and screen together, by the cannon

Helpmates in xiangqi

4 moves

Black moves first and both sides cooperate: Black, Red, Black, Red, and Red's second move mates. Black has 3 legal first moves and exactly one of them works. 4 pieces, Black 0 to Red 6.5 in material, mate by the cannon. Themes: cannon and screen together, the general walks in, a…