Wow, i did not see Qxb7, but white can not make that move because it's checkmate, all moves are forced
- ... Rxe3+
- fxe3 Qc2+
- Kf3 Be6
- Qxb7 Qf5+
- Ke2 (if 5. Kg3 Be5+ 6. Kh4 Qg4#) Bxc4+
- Kd1 (or Ke1 it is indifferent) Qd3+ (Bc3+)
- Kc1 (Kd1) Qc3+ (Qd3+)
- Kd1 (Kc1) Rd8+ (Qd2+)
- Qd7 (Kb1) Rxd7# (Bd3#)
RE: Chess problem 50 / Schachaufgabe 50