Checkmate: Impossible
Sort:
Nf7+ is also correct 
1.Rb8 Qh1+ now what? 1.Nf7+ blacks only move Rxf7 2.Rb8+ Rf8 3.Rxf8# I think you have puzzle solution backwards.
Stupid post. Nf7 was the only way to win, Rb8???
loses to some queen checks! nf7 doesn't allow black to do anything but sit an wait for death
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Oops nevermind
Trying to see if Black has a chance to win.
I'm not a good player, so it might be wrong.
At 3. Kg5 a Qg1 gets the #
Nf7+ mates. Rb8 loses to Qh1+
good puzzzle , but solution is wrong.
sorry about it 
only answer wasNf7
This was a mistake sorry :)
tis ok