Correct answer: Nc61...a2 2.R:a2# 1.Kd8?? zz 1...a2 2.R:a2# but 1...a:b4! 1.Kc7?? zz 1...a2 2.R:a2# but 1...a:b4! 1.Ke7?? zz 1...a2 2.R:a2# but 1...a:b4! 1.K