Correct answer: Rff11...Kb1 2.O-O# 1...d:e2 2.K:e2# 1.g3?? zz 1...Kb1 2.O-O# 1...d:e2 2.K:e2# but 1...f:g3! 1.g4?? zz 1...Kb1 2.O-O# 1...d:e2 2.K:e2# but 1...f:g3 e.p.!
