The alternative would have been 14...P - Kt 4; 15 B - B 2, P - Kt 5; 16 Kt - Q R 4, Kt (B 4) - K 5.
| | 15. Kt × Kt | P - Kt 4 |
| | 16. R × R | Q × R |
| | 17. Kt - B 3 | Q - B 5 |
Black aims at the exchange of Queens in order to remain with two Bishops for the ending, but in this position such a course is a mistake, because the Bishop at Kt 2 is inactive and cannot come into the game by any means, unless Black gives up the isolated Queen's Pawn which the Bishop must defend.
Not, of course, R - Q 4, because of Q × Q; Kt × Q, R - B 1; and there would be no good way to prevent R - B 7.
| | 18. ........ | Q × Q |
| | 19. Kt (B 3) × Q ! | |
Notice the co-ordination of the Knights' moves. They are manœuvred chain-like, so to speak, in order to maintain one of them, either at Q 4 or ready to go there. Now White threatens to take the open file, and therefore forces Black's next move.