Clearly that it is necessary to save Bb8. However, it is not clear as it to make. Exact calculation is necessary. Correct chose:
[Wrong try 1.Bc7!?
) 3...Rb7= ; 1.Be5!?
Nxb4= ] 1...Rxb4+
2.Nf8+ leads to main line]
2.Kxc1 Kg7 main B [main A 2...Rb7 3.Nf8+ Kh6 4.Be3+ Kg7 5.Ne6+ Kxf7 6.Nd8++-]
3.Be8 Kf6 4.Kd1!! important key move. wK should not leave the first rank. Again are several main lines here: [Wrong try 4.Kd2!? Rg4 5.Nf8 Ke7 6.Bh5 Rg2+= ] 4...Rc4 main B3 [also B1 4...Re4 5.Bb5 Kxg6 6.Bd3 Kf5 7.Bb8+- , or B2 4...Rg4 5.Nf8 Ke7 6.Bh5 Rg5 7.Ng6+ Kf7 8.Nf4++- ] 5.Bb5 Rc7 6.Bb6! Rb7 7.Nf8 Ke7 (also7...Rxb6 8.Nd7++- and 7...Kg7 8.Nd7+- ) 8.Bc5++-