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of action of the White pieces, as they must always be ready for the defence of the threatened pawns, and this gives Black by far the superior game.
The play was continued as follows: 1. ... R-Kt1; 2. BxP, R-Kt7; 3. B-K4, B-K3; 4. P-QR3, KR-Kt1. The Knight's file is now definitely in Black's hands. White could occupy the Queen's file, but the Black B at K3, which prevents the entry of the Rooks at Q7, makes the operation aimless. Therefore White is condemned to inactivity. On the contrary, Black's line of action is clear. His entry on the seventh can only achieve something if White's QBP can be deprived of its support. To do this Black has only to play P-QB4-B5 and P-KB4. This, of course, weakens Black's KB, and the White Rooks might obtain an entry on the K file. Therefore Black will effect a timely exchange of one of his Rooks, after which his King alone will hold the K file. These considerations make the following moves clear: 5. KR-K1, P-QB4; 6. P-KR3, a further awkward necessity in positions of this kind. Before the Rook can venture out, a loophole must be provided for the King.
6. ... P-B5; 7. R-K3, R-Kt8ch; 8. RxR, RxRch; 9. K-R2, P-B4; 10. B-B3, K-B2; 11. B-K2 (threatening R-QB3), R-Kt2; 12. R-QB3, K-B3 (now BxP is not feasible on account of R-QB2); 13. P-B4. White wishes to keep the Black King from his Q5 but cannot do so permanently. Black, however, can occupy the Q file with his Rook, and confine the White King to his wing. 13. ... R-Q2; 14. K-Kt3) R-Q5; 15. K-B3, K-K2; 16. R-K3, K-Q3; 17. K-Kt3, R-Q7; 18. P-B3, B-B2. R-R7 would be a mistake on account of RxBch, but the QRP cannot escape. 19. P-QR4, P-Kt3; 20. B-B3, R-R7; 21. B-Q1, B-Q4; 22. R-K2, R-R8; 23. R-Q2, R-R6; 24. R-QB2, RxRP. Now at last Black has obtained material gain, which was made possible by his command of the open Kt file. To convert it into a win by queening the extra pawn is only a matter of time.
We have now seen how the possession of open files reacts on the mobility of the opposing forces, forever increasing t
