30 Dec '21 21:48>
In Geller-Reshevsky (Zurich Candidates, 1953), the following position was reached after 15...Nc6-a5.
Here, White played 16. Be7, and the game ended in a draw.
In his book on the tournament (translated by Oscar D. Freedman), David Bronstein says that after 16. Qd2 [so that 16...Qxf6 17. Qxa5 would give White a slightly better endgame], 16...Re8 would fail because of 17. Be5, and if 17...Nc4 then 18. Qh6, "and if now ...Nxe5 or ...f6 White answers Ng5 anyway." We'll first consider the sequence ending with 18...Nxe5 19. Ng5. (See next diagram.)
19...Qxd4 would remove the attacker of Black's knight (which protects f7 and thereby prevents Qxh7+ Kf8 from being followed by Qxf7 mate) while pinning White's f-pawn. Then 20. Rae1 (threatening 21. Rxe5) 20...Be6 (on 20...Qf4, 21. Qxh7+ Kf8 22. Qh8+ Ke7 23. Rxe5+ regains the material while keeping an attack) 21. Qxh7+ Kf8 22. Qh8+ Ke7 23. Qxe5 Qxe5 24. Rxe5 Rac8 25. Rfe1 Kf6 26. h4 Rc2 27. R1e2 Rxe2 28. Rxe2 Rc8 seems perhaps a tad better for Black in light of his control of the c-file. (See next diagram for the sequence from 16. Qd2 to 28...Rc8.)
However, after 16. Qd2 Re8 17. Be5 Nc4 18. Qh6 Nxe5, White should simply recapture by 19. dxe5. Then 19...f6 (to clear the second rank for defense of Black's h-pawn) 20. exf6 Qxf6 21. Ng5 Qg7 22. Qxg7+ Kxg7 23. Rac1 Re7 24. Rfd1 h6 25. Nf3 Be6, with White somewhat better owing to his more harmonious pieces. (See next diagram for the sequence from 16. Qd2 to 25...Be6.)
The second sequence implied by Bronstein's note ends with 18...f6 19. Ng5 and is depicted in the next diagram.
After 19. Ng5, Black's pawn is constrained from taking either piece: the knight is immune because Black's f-pawn is pinned against the g7-square, and the bishop can't be taken because of the threat Qh7+ followed by Qf7 mate. If Black replies with 19...Re7, play might continue as depicted in next diagram (which starts with 19. Ng5).
After 18...f6 19. Ng5, another viable defense would be 19...Nxe5, with one plausible continuation being given in the next diagram (which again starts with 19. Ng5).
Conclusion: After 16. Qd2, 16...Re8 intending 17. Be5 Nc4 18. Qh6 f6 seems satisfactory for Black.
Here, White played 16. Be7, and the game ended in a draw.
In his book on the tournament (translated by Oscar D. Freedman), David Bronstein says that after 16. Qd2 [so that 16...Qxf6 17. Qxa5 would give White a slightly better endgame], 16...Re8 would fail because of 17. Be5, and if 17...Nc4 then 18. Qh6, "and if now ...Nxe5 or ...f6 White answers Ng5 anyway." We'll first consider the sequence ending with 18...Nxe5 19. Ng5. (See next diagram.)
19...Qxd4 would remove the attacker of Black's knight (which protects f7 and thereby prevents Qxh7+ Kf8 from being followed by Qxf7 mate) while pinning White's f-pawn. Then 20. Rae1 (threatening 21. Rxe5) 20...Be6 (on 20...Qf4, 21. Qxh7+ Kf8 22. Qh8+ Ke7 23. Rxe5+ regains the material while keeping an attack) 21. Qxh7+ Kf8 22. Qh8+ Ke7 23. Qxe5 Qxe5 24. Rxe5 Rac8 25. Rfe1 Kf6 26. h4 Rc2 27. R1e2 Rxe2 28. Rxe2 Rc8 seems perhaps a tad better for Black in light of his control of the c-file. (See next diagram for the sequence from 16. Qd2 to 28...Rc8.)
However, after 16. Qd2 Re8 17. Be5 Nc4 18. Qh6 Nxe5, White should simply recapture by 19. dxe5. Then 19...f6 (to clear the second rank for defense of Black's h-pawn) 20. exf6 Qxf6 21. Ng5 Qg7 22. Qxg7+ Kxg7 23. Rac1 Re7 24. Rfd1 h6 25. Nf3 Be6, with White somewhat better owing to his more harmonious pieces. (See next diagram for the sequence from 16. Qd2 to 25...Be6.)
The second sequence implied by Bronstein's note ends with 18...f6 19. Ng5 and is depicted in the next diagram.
After 19. Ng5, Black's pawn is constrained from taking either piece: the knight is immune because Black's f-pawn is pinned against the g7-square, and the bishop can't be taken because of the threat Qh7+ followed by Qf7 mate. If Black replies with 19...Re7, play might continue as depicted in next diagram (which starts with 19. Ng5).
After 18...f6 19. Ng5, another viable defense would be 19...Nxe5, with one plausible continuation being given in the next diagram (which again starts with 19. Ng5).
Conclusion: After 16. Qd2, 16...Re8 intending 17. Be5 Nc4 18. Qh6 f6 seems satisfactory for Black.