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Under FIDE law 9.3.1, a player to move may claim a 50-move draw by writing down the intended 50th move and making the claim.
Supposing this claim is otherwise valid; if the move would checkmate then is the game drawn?
Mate ends the game immediately, but the mating move must be made, not just written down. If the player only writes the move down and claims a draw in the correct way, it's a draw (but I doubt it'll ever happen in practice).