If you know how to play chess, it's not a hard move. Especially since it's telling you that you have a checkmate opportunity and the only two pieces that can be moved near White King are the Black Knight and Black Queen.
Yeah, it's telling you you have checkmate in one move, so finding it ain't hard. I'm a shitty chess player (literally only know how pieces are allowed to move, nothing about strategy) and it took me less than 30 seconds.
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