Black offers the exchange in order to get rid of White’s QB. If White accepts the sacrifice, he loses his KKtP, and Black retains three passed pawns for the piece, at least an equivalent for the end-game. White should decline the doubtful gift and meet the threat of P-R3 and P-KKt4 with 19. R-KKt1.
19. B-Q4 P-R3 20. B-B6ch K-B2 21. BxR RxB 22. R-Q1
in order to play 23. B-Q7 in answer to P-B4. This explains White’s check at move 20.
22. … PxPch 23. K-Kt2 K-B3!
If now 24. Kt-Q5ch, Black would assail the White King with K-K4; 25. KtxP, B-B5-K7-B6. The Black phalanx of pawns becomes menacing.
24. B-Kt3 BxB
25. RPxB K-K3
26. P-Kt4 R-R2
Black need no longer fear to exchange Rooks, for he would then threaten the Queen’s side pawns with his King whilst the passed pawns kept the White forces occupied.
27. Kt-K2 R-Q2 28. Kt-Q4ch K-B3 29. P-QB3 P-B3
The aim of this move is not clear. Black should adopt a forward policy with P-Kt5, P-B5, R-R2, etc.
30. R-KR1 P-Kt5 31. R-R8