user4223: 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?

user7297: 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).

4223: <p>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.</p>

<p>Supposing this claim is otherwise valid;  if the move would checkmate then is the game drawn?</p>
 7297: <p>Mate ends the game immediately, but the mating move must be <em>made</em>, 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).</p>
