Now to the analysis...

**1. e4 Nf6 2. e5 Nd5 3. c4 Nb6 4. c5 Nd5 5. Bc4 e6
6. Nc3 d6**

**7. Nxd5**

7. cxd6 Nxc3 (7...cxd6 8. Nxd5 exd5 9. Bxd5 dxe5 10. Qb3, and the queen/bishop "battery" is annoying for Black) 8. bxc3 (8. dxc7 Qxc7 leaves White down a piece) 8...cxd6, and Black is fine.

**7...exd5 8. Bxd5 dxe5 9. Qf3**

This supposedly refutes Black's eighth move, but theory does not consider the following idea.

**9...f5! 10. Bxb7 e4 11. Qb3 Bxb7 12. Qxb7 Nd7**

By sacrificing a pawn to exchange light-square bishops, Black has gained control over the d3-square and hopes to soon plant the knight there. We now examine

A) **13. Qc6**

B) **13. b4**

C) **13. Qd5**

D) **13. Nh3**

E) **13. d4**

A) **13. Qc6**

**13...Be7**

13...Bxc5 14.Nh3, when 15. Nf4 or 15. Ng5 are a nuisance. The c5-square is best reserved for Black's knight.

**14. Nh3 0-0 15. Nf4 Nxc5 16. Ne6 Nxe6
17. Qxe6+ Kh8**

White's backward d-pawn remains a problem.

B) **13. b4**

**13...a5 14. bxa5**

14. a3 axb4, and the a-pawn is pinned. 14. Ba3 axb4, and White cannot safely recapture (15. Bxb4 Rb8; 15. Qxb4 Bxc5). 14. c6 Ne5 15. bxa5 Nd3+ 16. Ke2 Rb8 17. Qa7 Bc5 18. Qa6 Qd4 wins material.

**14...Rxa5**

Black regains the pawn and maintains activity, as 15. c6 is disasterous after 15...Nc5 16. Qb1 Nd3+ 17. Ke2 Bc5 18. Nh3 Bd4.

C) **13. Qd5**

Hoping to coax 13...g6 14. c6 Nf6, which would derail Black's Nd7-c5-d3 idea.

**13...Nxc5**

Not 13...Be7 14. b4 a5 15. c6, which would force the knight to where it lacks ready access to the d3-square.

We now examine

C1) **14. Qxf5**

C2) **14. Qc6+**

C3) **14. Qe5+**

C1) **14. Qxf5**

**14...Be7 15. Nh3**

This bolsters the f2-square in anticipation of ...Rf8.

**15...g6 16. Qg4 Nd3+ 17. Ke2 Qd4 18. Qg3**

Intending to answer 18...Rd8 by 19. Qe3. 18. Rd1 (anticipating Black's attack on the d-pawn) 18...Qc4, and White has no good defense to 19...Nxc1+.

**18...Qc4**

18...Bf6 is also not bad, with the idea of 19...Qc4 20. Kd1 Bxb2 21. Bxb2 Nxb2+ 22. Ke1 Nd3+ and 23...Rb8. Either way, White has difficulties.

C2) **14. Qc6+**

**14...Kf7 15. Nh3 Nd3+ 16. Ke2 Be7 17. Qc4+ Kf8 18. Rf1**

Preparing 19. f3, to contest Black's control of the d3-square while opening a file against Black's king.

**18...Qd6**

Black stands well, as 19. f3 would give White another pawn island after 19...Ne5 and 20...exf3+.

C3) **14. Qe5+**

**14...Be7 15. Qxg7**

15. Qxf5 would invite 15...Rf8 and 16...Nd3+.

**15...Bf6 16. Qh6**

16. Qg3 Nd3+ 17. Ke2 Qd4 18. Nh3 (18. Qe3 Qc4 19. Kd1 Bd4) 18...Qc4 19. Kd1 Bxb2 20. Bxb2 Nxb2+ 21. Ke1 Nd3+ 22. Kd1 Rb8.

**16...Nd3+ 17. Ke2 Bg5 18. Qh5+**

18. Qg7 loses to 18...Nxc1+.

**18...Kf8 19. Kf1! Nf4**

19...Nxc1 20. Rxc1 Qxd2 21. Ne2 (21. Rxc7 results in the deactivation of White's queen after 21...Qd3+ 22. Qe2 Qb1+ 23. Qe1 Qxb2) 21...Rd8 22. g3, threatening 23. h4 or 23. Rxc7.

**20. Qd1 Qd3+ 21. Ne2 Rd8**

Black has ample compensation and could regain the pawn at will, by ...Nxe2 followed by ...Bxd2. 21...Nxg2, intending 22. Kxg2 Qf3+ 23. Kg1 Rg8, would have been refuted by 22. Rg1.

D) **13. Nh3**

**13...Nxc5**

13...Be7 14. d4 might enable White to improve over line E, since Black's bishop's would have already expended a tempo on the way to capturing the c-pawn.

**14. Qc6+ Kf7 15. Nf4**

15. Ng5+ leaves White defenseless after 15...Qxg5 16. Qxa8 Qxg2 17. Qd5+ Kg6.

**15...Be7 16. b4**

16. 0-0 Qd6 forces the exchange of queens, eliminating White's potential counterplay against Black's exposed king.

**16...Nd3+ 17. Nxd3 Qxd3**

White's light-square weaknesses persist. 18. Qxc7 can be met by 18...Rhc8, with ample compensation for Black.

E) **13. d4**

To free the bishop and conceal the weakness of the d3-square, at the cost of creating possible outposts for Black on the c2- and e2-squares.

**13...exd3**

And now

E1) **14. Nf3**

E2) **14. Qd5**

E3) **14. Be3**

E1) **14. Nf3**

**14...Rb8 15. Qxa7 Bxc5**

Stronger than 15...Qe7+ 16. Be3 f4 17. c6.

**16. Qa4**

The only safe retreat that controls the f4-square.

**16...Qe7+ 17. Be3 Bxe3 18. fxe3 Qxe3+ 19. Kf1 Rxb2**

Winning, as 20. Re1 would be met by 20...Rf2+ 21. Kg1 Re2+ and mate next.

E2) **14. Qd5**

**14...Bxc5**

It's not clear what Black has after 14...Nxc5 15. Qxf5 Be7 16. Nf3. With a Black pawn at d3, a knight at c5 loses much of its point.

**15. Qxd3**

15. Qxf5 Qe7+ would be painful. 15. Bg5 would be defused by 15...Be7, but not 15...Bb4+ because of 16. Kd1 Be7 17. Bxe7, when 17...Qxe7 would not be check. 15. Nf3 Qe7+ 16. Be3 0-0-0 17. Nd4 Bxd4 18. Qxd4 Nb6, with Black's retaining the extra pawn.

**15...Qe7+**

Protecting the bishop in preparation for a possible ...Ne5. Black's active pieces offset the extra "pawn island."

E3) **14. Be3**

**14...Rb8**

14...Bxc5 15. Bxc5 Nxc5 16. Qc6+ Nd7 would deactivate Black's knight. There's no urgency to capture White's c-pawn.

We now examine

E31) **15. Qd5**

E32) **15. Qc6**

E33) **15. Qxa7**

E31) **15. Qd5**

**15...Nxc5**

15...Rxb2 loses to 16. c6, with a latent fork at e5.

**16. Qxf5**

16. Qc6+ Qd7 (Illustrating one of the points of 14...Rb8—to free the Black queen from having to protect the rook.) 17. Qxd7+ Kxd7 18. 0-0-0 Ke6, and White must work to regain the pawn; this is also the case for 16. Qe5+ Qe7.

**16...d2+**

Clearing the d3-square for the knight.

**17. Kd1**

17. Bxd2 allows 17...Rxb2, as 18. Qe5+ and 19. Qxb2 loses to 19...Nd3+.

**17...Nd3 18. Qe4+ Be7 19. Bd4**

The checks run out after 19. Qc6+ Kf8 20. Qf3+ Bf6.

**19...Nxb2+ 20. Bxb2 Rxb2 21. Qc6+ Qd7**

With advantage, for 22. Qa8+ Kf7 23. Qxh8 would lose to 23...Qa4+.

E32) **15. Qc6**

**15...Rxb2 16. Bd4**

16. 0-0-0 Rc2+ demonstrates the value of the d-pawn.

**16...Rc2**

16...d2+ 17. Kd1 Qb8, and the rook is immune because White's rook would then be lost, but 18. Qe6+ makes a mess of things. The saner text move seems to maintain a persistent extra pawn.

E33) **15. Qxa7**

**15...Rxb2 16. Qa3 d2+ 17. Kd1**

17. Bxd2 Nxc5 (preventing 18. Qxb2, due to 18...Nd3+), and Black's pieces would get very active.

**17...Qb8 18. Qd3**

To prevent 18...Rb1+.

**18...Qb4**

Threatening 19...Qa4+ 20. Ke2 d1(Q) mate.

**19. Bxd2 Nxc5 20. Qe2+**

White would lose material after 20. Bxb4 Nxd3.

**20...Qe4 21. f3 Qxe2+ 22. Nxe2**

White seems to have neutralized Black's initiative and obtain even chances.

Conclusion: 9...f5 appears to fully rehabilitate 8...dxe5.