A line in the King's Indian Defense runs 1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. Be2 O-O 6. Nf3 e5 7. O-O Nc6 8. Be3 Re8 9. d5 Nd4,

the tactical justification being 10. Nxd4 exd4 11. Bxd4 Nxe4.

Recently I began to wonder whether ...Nd4 might be playable even after the more usual 8. d5, producing the following position.

This article focuses on the position reached by White's acceptance of the sacrifice by 9. Nxd4 exd4 10. Qxd4, followed by Black's sharpest reply, 10...Re8.

Given his opponent's lack of obvious structural weaknesses, Black must play forcibly to obtain compensation for the pawn. In some variations, the resulting tactics extend into the endgame.

Black benefits substantially from his e-pawn's disappearance. The half-open file allows Black to exert vigorous pressure against White's pawn, forcing some of White's pieces to awkward squares, and the lever ...f5 often brings things to a head. The open a1/h8 diagonal means that if Black can establish material equality, his dark square bishop will be no liability in an ending, a refreshing distinction from the usual lines of the Classical Variation. Finally, the e5 square can be utilized by any of several Black pieces.

To be fair, the disappearance of Black's e-pawn gives White some assets too, namely the d4 square and a1/h8 diagonal. But these prove difficult for White to exploit.

After 10...Re8, we examine two moves that thwart the immediate threat of 11...Nxe4.

A. 11. Bg5
B. 11. Qd3

A. 11. Bg5

11...h6

11...Nxe4 12. Qxe4 nets White at least a pawn in all variations.

12. Bxf6 Bxf6 13. Qd3 Qe7

We now consider:

A1. 14. f3
A2. 14. Bf3

A1. 14. f3

14...Be5

14...Bg5 15. f4 Bf6 16. Bf3 consolidates. The text preserves the restraint of 15. f4 because of 15...Bxc3 and the capture of the e-pawn.

15. Rae1 f5 16. exf5

Else 16...f4 is stifling.

16...Bxf5 17. Qd2 Bxc3 18. Qxc3 Qe3+ 19. Qxe3 Rxe3 20. Kf2 Rae8 21. Bd1

21...Bd3 22. Rxe3 Rxe3 23. Rg1

23. Kxe3 Bxf1 forks two pawns.

23...Re5 24. b3 b5 25. cxb5 Bxb5

Black will finally regain the pawn. A remarkable illustration of the tactical resources available to Black in this line.

A2. 14. Bf3

With the idea of g3, Bg2, f4 to mobilize the kingside pawn majority, against which Black must undertake immediate countermeasures.

14...Bg5

The strategic value of this diagonal soon becomes apparent. By contrast, 14...Be5 would leave Black with inadequate compensation after 15. g3 f5 16. exf5 Bxf5 17. Qd2.

15. g3

15. R(either)e1 f5, and since the pin along the e-file prevents 16. exf5, White could not stop ...f4.

15...f5 16. exf5

Else 16...f4 is stifling.

16...Bxf5 17. Qd1 Qg7

Black has pressure for the pawn. 18. Qb3 is met by 18...Bd2 (threatening 19...Bxc3 to ruin White's queenside pawn position) 19. Qxb7 Bxc3 20. bxc3 Qxc3 21. Bg2 Qxc4 and Black seems okay.

B. 11. Qd3

11...Qe7

and now

B1. 12. Bg5
B2. 12. Bf3
B3. 12. f3

B1. 12. Bg5 h6 13. Bxf6 Bxf6

This has transposed into Variation A.

B2. 12. Bf3

Protects the pawn, keeps the two bishops and inhibits ...Nh5.

12...Nd7

To achieve ...f5, Black is obliged to block his light square bishop temporarily, but the immediate threat to obtain the two bishops gains back the lost tempi.

13. Qc2 Ne5 14. Be2 f5

15. exf5

15. f4 Nf7 regains the pawn, as 16. Bf3 Bxc3 17. Qxc3 fxe4 18. Re1 can be met by 18...Bf5 (19. g4 Qh4 and White's kingside is coming unglued). 15. f3 Nf7 16. Be3 (16. Bd3 Ne5 and White has nothing better than returning to the e2 square) Bxc3 17. Qxc3 fxe4 18. Rae1,

and White, fully mobilized and with two bishops in an open position, would seem to have a splendid position according to classical principles. Yet after 18...exf3 19. Bxf3 Ne5, it's not clear White has any edge at all; Black's entrenched knight blocks both a key file and the critical a1/h8 diagonal, giving him the time to finish his development.

15...Bxf5 16. Qd1 Qh4

Black's piece activity seems to fully compensate for the pawn. If White now tries 17. h3 (to keep Black's pieces out of the g4 square), Black draws by 17...Nxc4 18. g3 Qxh3 19. Bxc4 Bxc3 20. bxc3 Be4 21. f3 Qxg3+.

B3. 12. f3 Nh5

and now

B31. 13. Be3
B32. 13. g4

B31. 13. Be3 Be5

Threatening 14...Qh4 (15. g3 Nxg3; 15. h3 Bxh3).

14. f4

14. g3 permits Black a strong attack by 14...Bh3 and 15...Nxg3 16. hxg3 Bxg3, with ...Qh4 to follow. 14. Qd2 Qh4 15. f4 Bxc3 and 16...Rxe4 gives Black active play.

14...Bxc3 15. Qxc3 Nf6

15...Qxe4 is met by 16. Bd2, and White would soon dominate the a1/h8 diagonal, to Black's regret. 16...Qxe2 would get skewered by 17. Rae1.

16. e5

Opening the game for White's bishops.

16...dxe5 17. fxe5 Ne4

17...Qxe5 18. Bd4 Ne4 (else the knight is lost) permits 19. Qe3 followed by doubling on the e-file. The more precise text forces White's queen to move while the e3 square is still occupied.

18. Qd3 Qxe5 19. Bd4 Qe7

Black's pressure on the e-file and centralized knight offset his dark square weaknesses and White's unopposed dark square bishop. This position contrasts with that reached in the note to Black's 15th move.

B32. 13. g4 Nf6 14. Bg5

The point of 13. g4. The pin inhibits the ...f5 break.

14...h6 15. Bh4 g5 16. Bg3 h5

Since the ...f5 break isn't feasible, Black finds an alternative method of creating the necessary pawn tension.

17. h3

17. gxh5 would be very compromising to White's kingside, as well as loosening of the f5 square.

17...Nd7 18. Qd2 Ne5 19. Bd3

To meet 19...Ng6 with 20. Ne2, so that if 20...Nf4, White could eliminate that piece while retaining his dark square bishop which helps shore up White's kingside. 20...Ne5, threatening 21...Nxd3 followed by either ...Bxb2 or ...f5 (with the idea of meeting gxf5 by ...Bxf5, for if White then takes the bishop, his knight would be taken in return) and hoping for a repetition by 21. Nc3 Ng6, would be thwarted by 21. Nd4.

19...Qf6 20. Kg2 Qh6

Bad is 20...Ng6 because of 21. Ne2 h4 (so that the h-pawn isn't hanging when the smoke clears) 22. Bf2 Qxb2 23. Qxg5 Bf6 (to force the queen to a less aggressive spot) 24. Qe3 (24. Qh5 loses the exchange to 24...Qxe2 25. Bxe2 Nf4+ followed by ...Nxh5 and ...Bxa1) 24...Qxa1 25. Rxa1 Bxa1 26. f4, leaving Black's kingside in shreds.

After 20...Qh6, Black retains pressure. He can follow up with ...Ng6 and ...Be5 to weaken White's dark squares still further.

Conclusion: A clear path to a White advantage after 8...Nd4 was not found, but this analysis could hardly be claimed definitive. I shall refrain from the hackneyed plea for practical tests, though obviously I'd be delighted if some intrepid soul saw fit to try out the sacrifice.