Zugzwang...

yeah...Qxc3 then Nxc6#

nice

I'm sorry but why doesn't black play 2... a3? Doesn't every puzzle require the other side to make the best possible move?

Stupid. Look the move list and make sure of yourself before affirmating that there is a flaw in a chess problem.

yes but however 2... a3 leads to a slower mate than than 2... Qa3. That's what qualifies a3 as a 'better' move than Qa3, even if it loses the queen.

EDIT: please think your comments through and see if you are logical before insulting somebody else. Thanks!

Yeah, I'm confused as well, don't both 0...kxa6 and 2...a3 lead to a longer mate than in the puzzle making those moves "better" than the text moves? I see that black is lost without his queen but at least his king isn't mated yet.