1.Kc6
White needs to weave a mating net before the Black pawn queens - this threatens 2.Rxa7#, and there are two main lines: Variation [A]
1...a6
2.Rxd5+b5
3.Rd4g1=Q
4.Ra4+!bxa4
5.b4#
Variation [B]
1...Ka6
2.b4b5
3.a4bxa4
4.Rxd5any
5.Ra5+then
5.b5#
Duras (1926)