13.1.Rxg7+ Kh8 (Or 1...Kxg7 2.Rg1+ Kh6 3.Qf6+ Kh5 4.Qg5#) 2.Qf5 Kxg7 3.Rg1+ Kh8 (Or 3...Kh6 4.Qg5#) 4.Qf6#