Correct answer: Nd31...Nb8/Nc5/Nc7 2.Rc5# 1.a3?? zz 1...Nb8/Nc5/Nc7 2.Rc5# but 1...b:a3! 1.a4?? zz 1...Nb8/Nc5/Nc7 2.Rc5# but 1...b:a3 e.p.!