This one is more difficult than usual. White has multiple mating "nets" available.
Qxg6, if fxg6, then Bxe6. Both lead to a similar position but Nf4 is a "fighting to the death" move. All it seems to do is block the black squared bishop.
Be6+ is pretty straight forward, forces king onto an open file. Rf7 loses the rook.
Rh4 forces black's bishop to block with Bh6, but again this just prolonging the game in hopes white blunders.
If Rxh6 then the king has the g7 square. White's pieces would not be working together giving black time to bring the queen out.
Bg8 or Bxg8 are two mating threats. So, black has to play Rf5 to block it. This is the final move black can make to get a miracle. Black is throwing out whatever material they can to prolong the game in hopes white will blunder.
There is a thread in the puzzles forum of course, but it seems to be just people saying "bravo, great puzzle!" etc so I'm not sure that's the place where actual discussion is supposed to take place.
I literally don't get [i]even one single move[/i] from the puzzle. Most notably, I do not understand why it ends where it does. I can see that the opponent is in serious trouble, but what is the reason for putting the rook where it ends up at the end, threatened by the pawn? How did that improve the player's position?
And, well, just what the heck is going on in this puzzle in general? I didn't get the reasoning behind [i]any[/i] of it.
http://www.chess.com/forum/view/daily-puzzles/2212015---b-larsen-t-petrosian-santa-monica-1966