53. model mate, by the chariot

Helpmates in xiangqi

4 moves

Black moves first and both sides cooperate: Black, Red, Black, Red, and Red's second move mates. Black has 55 legal first moves and exactly one of them works. 15 pieces, Black 43 to Red 11 in material, mate by the chariot. Themes: pure mate, model mate, a piece already in the way…