Black to move, and win

Find black's move that leads to a win.

Originally posted by phgao
[fen]8/7p/1R4p1/P1p2pP1/2P2k2/1P5K/2r5/8 b - - 0 1[/fen]

Find black's move that leads to a win.

1 ..h6 looks good.

If white takes the pawn, black mates in 4.

2 gxh6 g5 3 Rg6 g4+ 4 Rxg4+ 4 fxg4+ 5 Kh4 Rh2++

Otherwise black can capture white's rook with:

2 Rxg6 hxg5 3 Rxg5 Kxg5

White cannot just try and promote his a-pawn as he doesn't have enough moves

2 a6 hxg5 3 a7 g4+ 4 Kh4 Rh2++