Normally, you can't take back a move. In this problem, you have to!
Since Black can kill White with A, Whites last move was a mistake.
1. Take back the last white move! (of course, you have to choose a move that gives you the chance to live instead, because...)
2. After that, play a better move that allows White to live.
I didn't know a suitable way to present a problem like this on this site. Does anybody know a better way to show a "retractor"?
(;GM[1]FF[4]CA[UTF-8]AP[CGoban:2]ST[2]
RU[Japanese]SZ[11]KM[0.00]
PW[Weiß]PB[Schwarz]AW[aj][bj][cj][bk][dk]AB[bi][ci][di][ei][ej][ek]LB[gi:b][hi:b][ii:b][ji:b][dj:A][gj:b][ij:w][jj:w][kj:w][gk:b][hk:w][jk:w]C[White to take his last move back (choose the corresponding point on the right), and play and live instead!]PL[W]
;W[jk]CR[jk]
;B[jc]LB[aa:b][ca:b][da:w][ea:b][ab:w][bb:w][cb:w][eb:b][bc:b][cc:b][dc:b][ec:b]CR[jc]C[Taking W B1 back is right, but only if you 'uncapture' (as the chess problemists named this) two black stones at A1 and C1. That gives the position in the top left. Now, please play there to live! ]
;W[db]LB[aa:b][ca:b][da:w][ea:b][ab:w][bb:w][cb:w][eb:b][bc:b][cc:b][dc:b][ec:b]CR[db]C[Very well :) Black can't play at B1(1) now, so White is alive. RIGHT])