This forum is for the discussion of the line 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4. This is not a very aggressive try for White and Black should equalize with little trouble.

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4 d5

A. 6.dxc5 dxc4 7.Qxd8+ Nxd8 gives easy equality

B. 6.Bxd5 is an interesting position. Theory recommends 6...Nxd4 with more complications after 7.Bxf7 or 7.Nxf7, but Fritz gives 6...Bb4+ 7.c3 Nxd5 with equality, for example 8.exd5 Qxd5 9.cxb4 Qxg2 10.Qf3 Qxf3 11.Nxf3 e4 12.Ng5 Nxb4 with an imbalanced, interesting position. Apparently, to prevent Black's Knight from occupying the outpost on d3 White must sacrifice a pawn, giving Black three pawns for a piece.

C. 6.dxe5 Nxe5 7.Bb3 Qe7 8.Bxd5 Bg4 9.f3 0-0-0 -+ because although Black will lose a pawn or two if White grabs material, his attack is more than powerful enough to make up for it.

D. 6.exd5 Nxd4 =/+ with material even, Black's development gives him an advantage

Sorry for the late reaction. Clearly, B is the critical line here. I'm not convinced of your piece sacrifice. It would be nice if we could make that work, but maybe we have to look at the main lines with 6...Nxd4.

I still think 15...0-0 would be fine for Black with that monstrous Knight and two pawns for a piece (16.Nxc7 Rac8 and Black gets open files for both Rooks too) but I'm afraid I don't have many lines or much time to find them for the other idea. Here's a vague sketch:

A: 7.Bxf7+ Ke7 8.Bc4 b5 9.Bd3 h6 (9...Rf8 is an interesting try. 10.Be3 h6 11.Nf3 Bg4 12.Nbd2 Qd6 with compensation i.e. 13.h3 Nxf3+ 14.gxf3 Be6 15.Qe2 a6) 10.Nf3 (10.c3? hxg5 11.cxd4 Qxd4 when white is having serious development problems. Black has a significant advantage here) 10...Bg4 11.Nbd2 Qd6 12.0-0 Rhf8 13.Nxd4 Bxd4 14.Be2 Bd7 15.Nf3 Bc5 16.Qxd6+ cxd6! and black has great compensation.

B: 7.Nxf7?! Qe7 8.Nxh8 Bg4 and white has four alternatives:

B1: 9.Qd2 Nxd5 10.exd5 (10.c3 Nf6 11.cxd4 Bb4 12.Nc3 Nxe4 13.Qc2 Nxc3 and white is under heavy attack) 10...Bf5 11.0-0 Nxc2 12.g4 Qh4 13.Qg5 Qxg4+ 14.Qxg4 Bxg4 15.Be3 Bxe3 16.fxe3 Nxa1 17.Na3 Ke7 18.Rf7+ Kd6 19.Rxg7 Be2 20.Nf7+ Kxd5 21.Rxh7 and black is better.

B2: 9.Bf7+? Kf8 10.f3 Nxe4 11.fxg4 Qh4+ 12.g3 Nxg3 13.Bg5 Qxg5 14.hxg3 Qe3+ 15.Kf1 Nf5 and black wins.

B3: 9.f3? Nxd5 10.fxg4 Nb4 11.Na3 Qh4+ 12.g3 Qh3 13.c3 Qg2 14.cxd4 Qxh1+ 15.Kd2 Qxe4 and white will not survive.

B4: 9.Qd3 Nxd5 10.c3 Nb4 11.cxb4 Bxb4+ 12.Nc3 (12.Bd2 0-0-0 and black has a crushing attack) 12...Qd7 13.Kf1 Bxc3 14.f3 (14.bxc3 Be2+) 14...Ba5 15.fxg4 0-0-0 and black has great pressure.

A comment by g2-g4 on chesspub regarding the above post.

A brief comment on Conquistador's post about 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4 d5 6.Bxd5 Nxd4 7.Nxf7?! Qe7 8.Nxh8 Bg4

Now critical is 9.Qd2 Nxd5 10.exd5 (10.c3

0-0-0!?

- instead of 10...Nf6 - 11.ed Rxd5 12.dc? ed+ -+, or 12.b4 Bxb4 13.cb Qxb4! 14.0-0 Ne2+ -+, or 12.h3 Qh4 13.cd Rxd4 -+) 10...Bf5 11.0-0 (11.d6!?) Nxc2 12.g4?! (12.Qe2) Qh4 and instead of 13.Qg5 White can force a draw with 13.fg Qg4+ 14.Kh1 Qf3+ =. The only winning attempt here is 12...Nd4 13.Kg2 Bxg4 14.f3 Bxf3 15.Rxf3 Nxf3 16.Kxf3 0-0-0, but it is unclear.

9.Bf7+ Kf8 10.f3? Nxe4 11.fxg4 Qh4+ 12.g3 Nxg3 13.Bg5 Qxg5 14.hxg3 Qe3+ 15.Kf1 Nf5 is won for Black as mate is inevitable. This was played in

Karlsen,H.-Nordby,B./corr. 1985

. However, there's one more move to be considered. 11.h4 "is a real try for saving the game" (Heisman). But it also fails. 11...Nf5! and now

12.Qd5? Bf2+ 13.Kd1 Rd8 -+ (

Hanison,B.-Kuijpers,GFM/corr. 1998

)

12.fe Bxd1 13.fe Bxc2 14.Nc3 Qd6 -+

12.Qd3 Bf2+ (Heisman only mentioned 12...Nf2 which is worse) 13.Kd1 Rd8 14.Bd5 Nf6 15.fg Rxd5 16.gf Rxd3+ 17.cd Qd7 -+

Sadly for Black, it's not the whole story.

10.Qd3!

and he can fix a draw with 10...Be2 11.Qh3 Bg4 12.Qd3 or continue 10...Rd8, but after 11.Nc3 White is coming back to life.

After 9.f3? Nxd5 10.fxg4 inclusion of 10...Nb4? is unnecessary: 11.0-0! and the game is not that clear. Better is immediate

10...Qh4+

with the rest as given by Conquistador (see

Kunze,F.-Giertz,A./corr. 1976

). Also, 10.fg is not the only White's option.

10.ed. Now Heisman gives 10...Bf5 as the main line, but what he suggests further is not convincing. Probably the most direct way for Black is again 10...Qh4+ 11.g3 (11.Kd2? Bf5 -+) 11...Qh3 12.fg Qg2 -+, transposing to 10.fg

10.h4!? is a silicon's choice and it is pretty consistent because of preventing Qe7-h4+. I'm not quite sure about Black's best response, probably 10...Nb4 11.c3 0-0-0 keeping very strong attack. After 11.Na3 in

Szabo,I.-Lehmann/corr. 1984

Black apprehensively played 11...h6? preparing castling and subsequently lost. But after 11...0-0-0 12.Bg5 is in fact loosing: 11...0-0-0! 12.Bg5 Qf8 13.Bxd8 Bxf3! -+

9.Qd3 Nxd5 10.c3 Nb4 11.cxb4 Bxb4+ 12.Nc3 Qd7 13.Kf1 Bxc3 14.f3 and Black has spectacular possibility

14...Bxf3! -+

, exposing enemy's king.

15.gf Qh3+ 16.Kf2 Ba5 followed by 17...Bb6

15.Kf2 and only now 15...Ba5 which after 16.gf Qh3 transposes to 15.gf.

Upd. Conquistador did not mention 8.c3 ("a real try", according to Heisman). Black should play 8...Bg4 trying to change game's flow back into 8.Nxh8 course, e.g. 9.Qd2 Nxd5 10.Nxh8 0-0-0 transposes to 8.Nxh8 Bg4 9.Qd2 9.Qd3 Nxd5 10.Nxh8 Nb4 transposes to 8.Nxh8 Bg4 9.Qd3 Only after 9.f3 there's no variant to transpose to. 9...Nxf3 10.gf Nxd5

B1: 7.Bxf7+ Ke7 8.Bc4 b5 9.Bd3 h6 (9...Rf8 is an interesting try. 10.Be3 h6 11.Nf3 Bg4 12.Nbd2 Qd6 with compensation i.e. 13.h3 Nxf3+ 14.gxf3 Be6 15.Qe2 a6) 10.Nf3 (10.c3? hxg5 11.cxd4 Qxd4 when white is having serious development problems. Black has a significant advantage here) 10...Bg4 11.Nbd2 Qd6 12.0-0 Rhf8 13.Nxd4 Bxd4 14.Be2 Bd7 15.Nf3 Bc5 16.Qxd6+ cxd6! and black has great compensation.

B2: 7.Nxf7?! Qe7 8.Nxh8 (8.c3 Bg4 9.f3 [9.Qd2 Nxd5 10.Nxh8 0-0-0 transposes to 8.Nxd5 Bg4 9.Qd2; 9.Qd3 Nxd5 10.Nxh8 Nb4 transposes to 8.Nxh8 Bg4 9.Qd3] 9...Nxf3 10.gxf3 Nxd5 11.Qxd5 [11.fxg4 Qxf7 12.Rf1 Nf4; 11.Qe2 Nf4 12.Bxf4 Bxf3 13.Qxf3 Qxf7 14.Nd2 Qxf4] 11...Qh4+ 12.Kd2 Qf2+ 13.Kd3 Bxf3 14.Kc4 Be7) 8...Bg4 and white has four alternatives:

B1A: 9.Qd2 Nxd5 10.exd5 (10.c3 0-0-0!? is untested) 10...Bf5 11.0-0 Nxc2 12.g4 (12.Qe2 may be better) 12...Qh4 (12...Nd4! 13.Kg2 Bxg4 14.f3 Bxf3 15.Rxf3 Nxf3 16.Kxf3 0-0-0) 13.Qg5 Qxg4+ 14.Qxg4 Bxg4 15.Be3 Bxe3 16.fxe3 Nxa1 17.Na3 Ke7 18.Rf7+ Kd6 19.Rxg7 Be2 20.Nf7+ Kxd5 21.Rxh7 and black is better.

B1B: 9.Bf7+? Kf8 10.f3? (10.Qd3! and black can go for the draw with 10...Be2 11.Qh3 Bg4 12.Qd3 or continue 10...Rd8, but after 11.Nc3 White is coming back to life) 10...Nxe4 11.fxg4 (11.h4 Nf5!) 11...Qh4+ 12.g3 Nxg3 13.Bg5 Qxg5 14.hxg3 Qe3+ 15.Kf1 Nf5 and black wins.

B1C: 9.f3? Nxd5 10.fxg4 Nb4? (10...Qh4+!) 11.Na3? (11.0-0) 11...Qh4+ 12.g3 Qh3 13.c3 Qg2 14.cxd4 Qxh1+ 15.Kd2 Qxe4 and white will not survive.

B1D: 9.Qd3 Nxd5 10.c3 Nb4 11.cxb4 Bxb4+ 12.Nc3(12.Bd2 0-0-0 and black has a crushing attack)12...Qd7 13.Kf1 Bxc3 14.f3(14.bxc3 Be2+) 14...Bxf3! 15.gxf3 (15.Kf2 Ba5 which 16.gxf3 Qh3 transposes) 15...Qh3+ 16.Kf2 Ba5 followed by 17...Bb6

C. 6.dxe5 Nxe5 7.Bb3 Qe7 8.Bxd5 Bg4 9.f3 0-0-0 -+ because although Black will lose a pawn or two if White grabs material, his attack is more than powerful enough to make up for it.

D. 6.exd5 Nxd4 =/+ with material even, Black's development gives him an advantage

B1 is the critical line. White should play 14.Qe1 (instead of the dubious 14.Be2) as suggested by Stefan Buecker, when white seems being just a pawn up with no great problems to solve.

9...Rf8 is also good for white after the simple 10.c3, and as long as white does not get greedy, say 10...Ng4 11.Nxh7?! Nf3+ 12.gf3 Nxf2 with a complicated game, and replies with the natural 11.Nh3, when both 11...Ne6 12.0-0 and 11...Nxf2 12.Bg5+ are better for white.

IMO black should probably look at the "bad" move 5...Nxd4: 6.Nxf7 Qe7 7.Nxh8 d5 8.c3 (8.Bxd5? is a well-known mistake: black is at least equal after 8...Bg4. 8.Be2 is interesting, though) 8...dc4 (8...Bg4? is a patzer's move- black is toast after the simple 9.f3) 9. cd4 Bxd4 and white is an exchange up after every sensible move (11.Qa4+, 11.Nd2, 11.Nc3), but black has a healthy position, and can hope for a draw. Actually Pinski is looking this position a bit in his 2 knights monograph, but as usual his analysis is rather shallow and inconclusive.

In short, 5.d4 might be less good than 5.Bxf7+ Ke7 and now either 6.Bb3 or 6.Bd5 (I prefer the former, but this is pretty much a matter of taste), but still black does not seem to have a decent way to equalize, and white's position is rather easy to play.

Even the utterly infamous Kloss variation (5...d5 6.ed5 Nb4!?) seems being a better practical try against the Polerio. The Traxler is just a pawn down for minimal (to non-existent) compensation, as long as white does not lose his mind and goes for the Nxf7?! cheapo.

This forum is for the discussion of the line 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4. This is not a very aggressive try for White and Black should equalize with little trouble.

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4 d5

A. 6.dxc5 dxc4 7.Qxd8+ Nxd8 gives easy equality

B. 6.Bxd5 is an interesting position. Theory recommends 6...Nxd4 with more complications after 7.Bxf7 or 7.Nxf7, but Fritz gives 6...Bb4+ 7.c3 Nxd5 with equality, for example 8.exd5 Qxd5 9.cxb4 Qxg2 10.Qf3 Qxf3 11.Nxf3 e4 12.Ng5 Nxb4 with an imbalanced, interesting position. Apparently, to prevent Black's Knight from occupying the outpost on d3 White must sacrifice a pawn, giving Black three pawns for a piece.

C. 6.dxe5 Nxe5 7.Bb3 Qe7 8.Bxd5 Bg4 9.f3 0-0-0 -+ because although Black will lose a pawn or two if White grabs material, his attack is more than powerful enough to make up for it.

D. 6.exd5 Nxd4 =/+ with material even, Black's development gives him an advantage

Sorry for the late reaction. Clearly, B is the critical line here. I'm not convinced of your piece sacrifice. It would be nice if we could make that work, but maybe we have to look at the main lines with 6...Nxd4.

1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 Bc5 5. d4 d5 6. Bxd5

Bb4+ 7. c3 Nxd5 8. exd5 Qxd5 9. cxb4 Qxg2 10. Qf3 Qxf3 11. Nxf3 e4 12. Ng5 Nxb4

13. Na3 Nd3+ 14. Ke2 Bf5 15. Nb5 h6 16. Nxc7+ Kd7 17. Nxf7 Kxc7 18. Nxh8 Rxh8 is just one line where I doubt black's compensation.

I still think 15...0-0 would be fine for Black with that monstrous Knight and two pawns for a piece (16.Nxc7 Rac8 and Black gets open files for both Rooks too) but I'm afraid I don't have many lines or much time to find them for the other idea. Here's a vague sketch:

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4 d5 6.Bxd5 Nxd4

A. 7.Nxf7 Qe7

A1. 8.Nxh8 Bg4 9.Qd3 is very complicated. Fritz gives 9...Nxd5 10.c3 with slight advantage to White.

A2. 8.c3 0-0 with various lines that appear to all lead to near equality, for example 9.cxd4 exd4 10.Bg5 c6 11.Bc4 Qxe4+

B. 7.Bxf7+ Ke7 8.Bc4 b5 9.Bd3 h6 with a position very similar to the Bxf7+ lines

Here is a thorough analysis of

6...Nxd4.A:

7.Bxf7+ Ke7 8.Bc4 b5 9.Bd3 h6(9...Rf8 is an interesting try. 10.Be3 h6 11.Nf3 Bg4 12.Nbd2 Qd6 with compensation i.e. 13.h3 Nxf3+ 14.gxf3 Be6 15.Qe2 a6)10.Nf3(10.c3? hxg5 11.cxd4 Qxd4 when white is having serious development problems. Black has a significant advantage here)10...Bg4 11.Nbd2 Qd6 12.0-0 Rhf8 13.Nxd4 Bxd4 14.Be2 Bd7 15.Nf3 Bc5 16.Qxd6+ cxd6! and black has great compensation.B:

7.Nxf7?! Qe7 8.Nxh8 Bg4and white has four alternatives:B1:

9.Qd2 Nxd5 10.exd5(10.c3 Nf6 11.cxd4 Bb4 12.Nc3 Nxe4 13.Qc2 Nxc3 and white is under heavy attack)10...Bf5 11.0-0 Nxc2 12.g4 Qh4 13.Qg5 Qxg4+ 14.Qxg4 Bxg4 15.Be3 Bxe3 16.fxe3 Nxa1 17.Na3 Ke7 18.Rf7+ Kd6 19.Rxg7 Be2 20.Nf7+ Kxd5 21.Rxh7and black is better.B2:

9.Bf7+? Kf8 10.f3 Nxe4 11.fxg4 Qh4+ 12.g3 Nxg3 13.Bg5 Qxg5 14.hxg3 Qe3+ 15.Kf1 Nf5and black wins.B3:

9.f3? Nxd5 10.fxg4 Nb4 11.Na3 Qh4+ 12.g3 Qh3 13.c3 Qg2 14.cxd4 Qxh1+ 15.Kd2 Qxe4and white will not survive.B4:

9.Qd3 Nxd5 10.c3 Nb4 11.cxb4 Bxb4+ 12.Nc3(12.Bd2 0-0-0 and black has a crushing attack)12...Qd7 13.Kf1 Bxc3 14.f3(14.bxc3 Be2+)14...Ba5 15.fxg4 0-0-0and black has great pressure.A comment by g2-g4 on chesspub regarding the above post.

A brief comment on Conquistador's post about

1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4 d5 6.Bxd5 Nxd4 7.Nxf7?! Qe7 8.Nxh8 Bg4Now critical is

9.Qd2Nxd5 10.exd5 (10.c3- instead of 10...Nf6 - 11.ed Rxd5 12.dc? ed+ -+, or 12.b4 Bxb4 13.cb Qxb4! 14.0-0 Ne2+ -+, or 12.h3 Qh4 13.cd Rxd4 -+) 10...Bf5 11.0-0 (11.d6!?) Nxc2 12.g4?! (12.Qe2) Qh4 and instead of 13.Qg5 White can force a draw with 13.fg Qg4+ 14.Kh1 Qf3+ =. The only winning attempt here is 12...Nd4 13.Kg2 Bxg4 14.f3 Bxf3 15.Rxf3 Nxf3 16.Kxf3 0-0-0, but it is unclear.

9.Bf7+Kf8 10.f3? Nxe4 11.fxg4 Qh4+ 12.g3 Nxg3 13.Bg5 Qxg5 14.hxg3 Qe3+ 15.Kf1 Nf5 is won for Black as mate is inevitable. This was played in. However, there's one more move to be considered. 11.h4 "is a real try for saving the game" (Heisman). But it also fails. 11...Nf5! and now

Sadly for Black, it's not the whole story.

and he can fix a draw with 10...Be2 11.Qh3 Bg4 12.Qd3 or continue 10...Rd8, but after 11.Nc3 White is coming back to life.

After

9.f3?Nxd5 10.fxg4 inclusion of 10...Nb4? is unnecessary: 11.0-0! and the game is not that clear. Better is immediatewith the rest as given by Conquistador (see

). Also, 10.fg is not the only White's option.

9.Qd3Nxd5 10.c3 Nb4 11.cxb4 Bxb4+ 12.Nc3 Qd7 13.Kf1 Bxc3 14.f3 and Black has spectacular possibility, exposing enemy's king.

Upd. Conquistador did not mention

8.c3("a real try", according to Heisman). Black should play8...Bg4trying to change game's flow back into 8.Nxh8 course, e.g.9.Qd2Nxd5 10.Nxh8 0-0-0 transposes to 8.Nxh8 Bg4 9.Qd29.Qd3Nxd5 10.Nxh8 Nb4 transposes to 8.Nxh8 Bg4 9.Qd3Only after

9.f3there's no variant to transpose to. 9...Nxf3 10.gf Nxd5An updated analysis of

5.d41.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 Bc5 5.d4 d5and now:A. 6.dxc5 dxc4 7.Qxd8+ Nxd8gives easy equalityB: 6.Bxd5 Nxd4B1:7.Bxf7+ Ke7 8.Bc4 b5 9.Bd3 h6(9...Rf8 is an interesting try. 10.Be3 h6 11.Nf3 Bg4 12.Nbd2 Qd6 with compensation i.e. 13.h3 Nxf3+ 14.gxf3 Be6 15.Qe2 a6)10.Nf3(10.c3? hxg5 11.cxd4 Qxd4 when white is having serious development problems. Black has a significant advantage here)10...Bg4 11.Nbd2 Qd6 12.0-0 Rhf8 13.Nxd4 Bxd4 14.Be2 Bd7 15.Nf3 Bc5 16.Qxd6+ cxd6! and black has great compensation.B2:7.Nxf7?! Qe7 8.Nxh8 (8.c3 Bg4 9.f3 [9.Qd2 Nxd5 10.Nxh8 0-0-0 transposes to 8.Nxd5 Bg4 9.Qd2; 9.Qd3 Nxd5 10.Nxh8 Nb4 transposes to 8.Nxh8 Bg4 9.Qd3] 9...Nxf3 10.gxf3 Nxd5 11.Qxd5 [11.fxg4 Qxf7 12.Rf1 Nf4; 11.Qe2 Nf4 12.Bxf4 Bxf3 13.Qxf3 Qxf7 14.Nd2 Qxf4] 11...Qh4+ 12.Kd2 Qf2+ 13.Kd3 Bxf3 14.Kc4 Be7)8...Bg4and white has four alternatives:B1A:9.Qd2 Nxd5 10.exd5(10.c3 0-0-0!? is untested)10...Bf5 11.0-0 Nxc2 12.g4(12.Qe2 may be better)12...Qh4 (12...Nd4! 13.Kg2 Bxg4 14.f3 Bxf3 15.Rxf3 Nxf3 16.Kxf3 0-0-0)13.Qg5 Qxg4+ 14.Qxg4 Bxg4 15.Be3 Bxe3 16.fxe3 Nxa1 17.Na3 Ke7 18.Rf7+ Kd6 19.Rxg7 Be2 20.Nf7+ Kxd5 21.Rxh7and black is better.B1B:9.Bf7+? Kf8 10.f3? (10.Qd3! and black can go for the draw with 10...Be2 11.Qh3 Bg4 12.Qd3 or continue 10...Rd8, but after 11.Nc3 White is coming back to life)10...Nxe4 11.fxg4 (11.h4 Nf5!) 11...Qh4+ 12.g3 Nxg3 13.Bg5 Qxg5 14.hxg3 Qe3+ 15.Kf1 Nf5and black wins.B1C:9.f3? Nxd5 10.fxg4 Nb4?(10...Qh4+!)11.Na3?(11.0-0)11...Qh4+ 12.g3 Qh3 13.c3 Qg2 14.cxd4 Qxh1+ 15.Kd2 Qxe4and white will not survive.B1D:9.Qd3 Nxd5 10.c3 Nb4 11.cxb4 Bxb4+ 12.Nc3(12.Bd2 0-0-0 and black has a crushing attack)12...Qd7 13.Kf1 Bxc3 14.f3(14.bxc3 Be2+)14...Bxf3! 15.gxf3(15.Kf2 Ba5 which 16.gxf3 Qh3 transposes)15...Qh3+ 16.Kf2 Ba5followed by17...Bb6C. 6.dxe5 Nxe5 7.Bb3 Qe7 8.Bxd5 Bg4 9.f3 0-0-0-+ because although Black will lose a pawn or two if White grabs material, his attack is more than powerful enough to make up for it.D. 6.exd5 Nxd4=/+ with material even, Black's development gives him an advantageB1 is the critical line. White should play 14.Qe1 (instead of the dubious 14.Be2) as suggested by Stefan Buecker, when white seems being just a pawn up with no great problems to solve.

9...Rf8 is also good for white after the simple 10.c3, and as long as white does not get greedy, say 10...Ng4 11.Nxh7?! Nf3+ 12.gf3 Nxf2 with a complicated game, and replies with the natural 11.Nh3, when both 11...Ne6 12.0-0 and 11...Nxf2 12.Bg5+ are better for white.

IMO black should probably look at the "bad" move 5...Nxd4: 6.Nxf7 Qe7 7.Nxh8 d5 8.c3 (8.Bxd5? is a well-known mistake: black is at least equal after 8...Bg4. 8.Be2 is interesting, though) 8...dc4 (8...Bg4? is a patzer's move- black is toast after the simple 9.f3) 9. cd4 Bxd4 and white is an exchange up after every sensible move (11.Qa4+, 11.Nd2, 11.Nc3), but black has a healthy position, and can hope for a draw. Actually Pinski is looking this position a bit in his 2 knights monograph, but as usual his analysis is rather shallow and inconclusive.

In short, 5.d4 might be less good than 5.Bxf7+ Ke7 and now either 6.Bb3 or 6.Bd5 (I prefer the former, but this is pretty much a matter of taste), but still black does not seem to have a decent way to equalize, and white's position is rather easy to play.

Even the utterly infamous Kloss variation (5...d5 6.ed5 Nb4!?) seems being a better practical try against the Polerio. The Traxler is just a pawn down for minimal (to non-existent) compensation, as long as white does not lose his mind and goes for the Nxf7?! cheapo.