Orthodox checkmate problems stipulate that White (or Black) makes the first move - the key - and checkmates the opponent in a specified number of moves no matter what they play. The stipulation is inviolable: mate must be accomplished in exactly the number of moves specified, no more, no fewer. There is only one correct key for each problem.
* Have a go at this challenging problem
* Video – solve 30 problems in 30 minutes ? (4:50)
👍 Chess.com puzzles – click on Training