DDG 4.Nc3 Nf6 5.f3

This is the "orthodox" DDG. By playing f3, White does not even try to recapture the sacrificed pawn, but aims at opening the f-file for the rook and getting a nice d3-square for the bishop.

Black should attack d4 and delay the exf3 capture. The best replies are popular 5...Bb4 and extremely dangerous 5...c5. White should be happy to meet any other move.

B	5...Bb4 (Kmoch Variation) 5...c5 (Keres Variation) 5...exf3 (Exchange Variation) 5...Nc6 5...e3 5...Various

5...Nc6

5...Nc6 6.d5 exd5 7.cxd5 Nb4 8.fxe4 Bc5 9.a3 Na6 10.Bb5+ Bd7 11.Qe2 O-O 12.Bg5 Bxb5 13.Qxb5 h6 14.Bh4 g5 15.Bf2 Bxf2+ 16.Kxf2 Ng4+, 0-1 in 29, Heikkinen - Kytöniemi, 1991 !. This is my most dreadful loss with the DDG -- and the only one in a 90 minutes game so far. Black immediately returned the pawn, and took the initiative. This was a good lesson.

6.Be3

6...exf3 7.Nxf3 Bb4 8.Bd3 O-O 9.O-O

9...Re8 10.Bc2 b6 11.Bg5 Bb7 12.Qd3 h6 13.Bxf6 Qxf6 14.Qh7+ Kf8 15.Ne5, 1-0 in 25, Heikkinen - Vehmanen, Zone 1996.
9...b6 10.Bc2 Bb7 11.Qd3 g6 12.Bg5, 1-0 in 27, Heikkinen - tonio2, Zone 1996.

6...Bb4 is clearly the most important line here. This position can be reached in various ways: any order of the last two moves -- White's f3 and Be3, Black's Nc6 and Bb4 -- is common.

A) 7.a3 Bxc3+ 8.bxc3

8...e5!
- 9.d5?! Ne7 10.Bg5 exf3 11.Nxf3 Qd6 12.Be2 c6 13.Bxf6 Qxf6 14.O-O Qd6 15.Ng5 f5 16.Qa4 O-O 17.Rad1 Qh6 18.Nf3 Qe3+ 19.Rf2 e4 20.d6 Ng6 21.d7 Bxd7 22.Rxd7 exf3 23.Bxf3 Ne5 24.Rxb7 Ng4 25.Rb2 Rab8 26.Qc2 Nxf2 0-1, Heikkinen - Genius 2, 1996. Very impressive positional game from Genius 2, whose ELO is claimed to be 2342 on 486/50-66 MHz; it is hardly weaker on my Pentium/166 MHz.
- 9.dxe5 Qxd1+ (9...Nxe5 10.Qxd8+ Kxd8 11.O-O-O+ Bd7 12.Bg5 exf3 13.Nxf3 Nxf3 14.gxf3 Ke7 15.Be3 =/+, but White has the bishop pair and can play draw) 10.Rxd1 Nxe5 11.Bf4 exf3 12.Bxe5 f2+ 13.Kxf2 Ng4+ 14.Kg3 Nxe5 15.Re1 f6 16.Nf3, draw in 27, Laucius - Genius 2, 1996 !.
8...O-O 9.Bg5 h6 10.Bh4. Note similarity with the Modern Main Line: 8...O-O. Here White has lost one tempo, due to Be3. However, the queen probably stands better on d1 than on a4! For example, the familiar pattern Bc2-Qd3 could now be created more quickly.
- 10...e3 11.f4 b6 12.Bd3 Bb7 13.Nf3 Na5 14.O-O Rc8 15.Ne5 Re8 16.Ng4, 1-0 in 60, Heikkinen - Harris, 1996.
- 10...g5 11.Bg3 Nh5 12.fxe4 Nxg3 13.hxg3 Kg7 14.Qh5, 1-0 in 30, Heikkinen - bonjour, Zone 1996.
9.Qc2 exf3 10.Nxf3
- 10...Re8 11.Rd1 (11.Bd3 e5 12.dxe5 Bg4 13.O-O-O +/-) Qe7 12.Bd3 e5 13.dxe5 Nxe5 14.O-O Nxc4 15.Bxc4 Qxe3+, 0-1 in 47, Montenero - Demetrius, 1997.
- 10...b6 11.Bd3 Bb7 12.O-O Na5 13.Ng5 g6 14.Nxe6 fxe6 15.Bxg6 hxg6 16.Qxg6+ Kh8 17.Bg5 Nxc4 18.Rxf6 Qxf6? (18...Be4! +/=) 19.Bxf6+ Rxf6 20.Qxf6+ Kh7 21.Qxe6 b5 22.Qd7+ Kg6 23.Rf1 1-0, Washburn - Grandmaster Chess, 1996.

B) 7.Qc2! O-O (7...Nxd4? 8.Bxd4 Qxd4 9.Qa4+ Nd7!? 10.Qxb4 Nc5 11.Nxe4 Qe3+ 12.Kd1! +/-) 8.O-O-O

8...exf3 9.Nxf3 Bxc3 10.Qxc3 h6 11.Bd3 Ng4 12.Bg1 Bd7 13.h3 Nf6 14.g4 Nh7?! 15.Be3 Ne7 16.Qc2 f5?! 17.Rhg1 g5 18.h4 Nc6 19.a3 Qe7 20.gxf5 exf5 21.Rde1 1-0, Heikkinen - Watson, DDGA 1996.
8...Qe7 9.Nxe4 a6 10.Bg5 Rd8 11.Ne2 Ba5 12.h4 Nb4 13.Qb1 b5 14.a3 Nc6 15.b4 Bb6 16.c5 Ba7 17.g4 a5 18.h5 h6 19.Nxf6+ gxf6 20.Bxh6 axb4 21.axb4 Bb8 22.g5 Ra4 23.gxf6 Qxf6 24.Rg1+ 1-0, Heikkinen - Young, Zone 1996.

C) 7.Qd2!? O-O 8.a3 Bxc3 9.Qxc3 Ne7 10.O-O-O Nf5 11.g4 with good attack, Heikkinen - Laucius, corr. 1996. Unfortunately, that game was never finished. Maybe a3 is not necessary, but it almost forces Black to exchange the bishop to the knight, thus giving White the bishop pair. If Black plays something else, like 8...Be7, White has good game after 9.fxe4: the open f-file and even material.

Alternatives are

7.fxe4 Nxe4 8.Qd3 Bxc3+ 9.bxc3 Qh4+ 10.g3 Nxg3 11.Nf3, 1-0 in 63, Heikkinen - Chessmaster 3000, 1995 .
7.Nh3? h6 (7...exf3) 8.Be2 O-O 9.g4 e5 10.d5 Nd4 11.Bxd4, 1-0 in 33, Heikkinen - Palmer, Zone 1996.
7.Qa4 looks pointless because Nc6 is already played.
7.Qb3 transposes.

5...e3

5...e3 is a simple way to give the pawn back immediately. White does not get the half-open f-file, but material is even.

6.Bxe3

6...Be7 7.f4 O-O 8.Nf3 c5 9.d5 Na6 10.Qd2 Nc7 11.O-O-O, 0-1 in 25, Bernat - Dobcsanyi, 1998.
6...Bb4
- 7.Bd3 O-O 8.Ne2 c5 9.O-O cxd4 10.Bxd4 Nc6 11.Bxf6 Qxf6 12.Bc2 b6 13.Qd3 Qh6 14.f4, 0-1 later, Heikkinen - Pirttilahti, 2001.
- 7.Ne2 transposes to 1.d4 d6 2.e4 Nf6 3.f3 d5 4.exd5 Nxd5 5.c4 Nf6 6.Nc3 e6 7.Be3 Bb4 8.Ne2 O-O 9.a3 Be7 10.Qc2 Nbd7 11.O-O-O c6 draw, Dlugy - Anand, 1990.

The Winckelmann-Reimer Gambit can also transpose to this line: 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.a3 Bxc3+ 5.bxc3 dxe4 6.f3! e3?! 7.Bxe3 Nf6 8.Bd3 Nd5 9.Bd2 Nd7 10.Ne2 O-O 11.O-O e5 12.c4 N5f6 13.c3 b6 14.Bg5 Bb7 15.Qc2, 1-0 in 31, Oeller - Pohl, corr. 1993.

The line is similar to the Langeheinecke Defence of the BDG, which arises after 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 e3, and may continue 5.Bxe3 e6 6.Bd3

6...b6 7.Nh3 Nbd7 8.Qe2 Bb4 9.a3 Bxc3+ 10.bxc3 Bb7 11.c4 (DDG Deferred) O-O 12.Ng5 c5 13.c3, Diemer - Kunerth, 1947. Note that by playing Nc3-bxc3-c4-c3, White loses a tempo compared to the DDG where c4 is played before Nc3.
6...Nbd7 7.f4 Nb6 8.Nf3 Nbd5 9.Nxd5 Nxd5 10.Bd2 c5 11.c4, Fuller - Dilworth, corr. 1965.
6...Bb4 7.Ne2 Nd5 8.Bf2 O-O 9.O-O Nd7 10.Ne4 e5 11.c4, Leisebein - Hasselbach, 1989.

Various

5...Be7 6.fxe4 Nc6 7.Be3 e5 8.d5 Na5 9.Nf3 O-O? 10.Nxe5 c6 11.Bd3 (+-) cxd5 12.exd5 Re8 13.O-O Bd6 14.Nxf7! Kxf7 15.Qh5+ Kf8 16.Qxh7 Rxe3 17.Bg6 Bc5 18.Qh8+ Ke7 19.Qxg7+ Kd6 20.Rxf6+ Re6+ 21.Kh1 Qxf6 22.Ne4+ Ke5 23.Nxf6 1-0, Heikkinen - Juntunen, 1996.
5...c6 6.fxe4 +/- is similar to the O'Kelly Defence of the BDG: 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 c6. Worse is 6.Bg5?! Be7 7.Be2 h6 8.Bh4 exf3 9.Nxf3 O-O 10.O-O Ng4 11.Bxe7 Qxe7 12.Qd3 Nd7 13.h3 Ngf6 14.Bd1 b6 15.Bc2 Ba6 16.b3 Rad8 17.Rae1 Nc5 18.Qe3 Nb7 19.Ne5 Qd6 20.Rd1 Ne8 21.Ne4 Qc7 22.Ng4 Nbd6 23.Nxh6+ gxh6 24.Nf6+ Nxf6 25.Qg3+ Kh8 26.Rxf6 Nf5 27.Qxc7 Kg7 28.Rxf5 exf5 29.Qf4 Bc8 30.Rd3 c5 31.Rg3+ Kh8 32.Qxh6# 1-0, Heikkinen - Kalle2000, Zone 1996.