: E21-1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Nf3 ( Kasparov Variation excluding 4 ... c5 5. g3, which is covered under E20 )

An example of a similar smothered mate in master-level play is the game between Edward Lasker ( White ) and Israel Horowitz ( Black ) in New York City, 1946, which went: 1. d4 Nf6 2. Nf3 d5 3. e3 c5 4. c4 cxd4 5. Nxd4 e5 6. Nf3 Nc6 7. Nc3 d4 8. exd4 exd4 9. Nb5 Bb4 + 10. Bd2 0-0 11. Bxb4 Nxb4 12. Nbxd4 Qa5 13. Nd2 Qe5 + 14. Ne2 Nd3 #.

If Black is not aiming for the Sveshnikov, the main alternative is to play 6 ... Bb4 in reply to 6. Ndb5.

The idea is that 3. d4 runs into 3 ... cxd4 4. Nxd4 Nf6 5. Nc3 e5, when Nb5 is prevented, and Black will equalize by playing ... Bb4 and ... d5 at some point.

However, 3. Nf3 is often played instead as a way of avoiding the Nimzo-Indian Defence ( which would follow after 3. Nc3 Bb4 ).

A rarer third option is 4 ... Bb4 +, which aims to exchange the less useful dark-squared bishop, though this line tends to leave Black with a slightly passive position.

After 5. b3, Black also has several playable alternatives to 5 ... Bb4 +, the most common of which is 5 ... Bb7 6.

Perhaps the most famous example of Boden's mate is the so-called Peruvian Immortal game, Canal – NN, simultaneous exhibition, Budapest 1934: 1. e4 d5 2. exd5 Qxd5 3. Nc3 Qa5 4. d4 c6 5. Nf3 Bg4 6. Bf4 e6 7. h3 Bxf3 8. Qxf3 Bb4 9. Be2 Nd7 10. a3 O-O-O ??

8. dxe3 Bb4 ) Bd6 is strong for Black.

First, the " Reversed Ruy Lopez " with 3 ... Bb4 is ruled out.

Then the typical 4 ... Ng4 may be met by 5. d4 exd4 6. Na4, when 6 ... Bb4 +, White's usual move in the mirror-image position, is impossible.

The best line for Black may be 3 ... Bc5 4. Nf3 d5 5. exd5 0-0 ( better than 5 ... e4 6. d4, when the normal 6 ... Bb4 is impossible ), and if 6. Nxe5, 6 ... Re8 7. d4 Bxd4!

cxd4 10. Rxd4 or 7 ... h6 8. Bh4 ( 8. Bf4 is also possible, aiming to keep the Bxh6 sacrifice possibility open, but allowing 8 ... Bb4 9. Bc4 Ne4 ) 8 ... Ne4 9. Nxe4 Bxh4 + 10. g3 Be7 11. Bg2, when White has some compensation for the pawn but the final verdict on the resulting positions is still yet to be reached.

After 3 ... e6, however, White cannot easily force a Blackmar – Diemer Gambit type position as 4. f3 Bb4 is awkward.

* 1. d4 d5 2. e4 e6 3. Nc3 Bb4 4. a3 Bxc3 + 5. bxc3 dxe4 6. f3 is the Winckelmann – Reimer Gambit.

Barden has said that " my favourite game " is his win against Weaver Adams ( Black ) at Hastings 1950-51: 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 d5 5. exd5 Nxd5 6. d4 Bb4 + 7. c3 Be7 8. Nxf7 Kxf7 9. Qf3 + Ke6 10. Qe4 Bf8 11. O-O Ne7 12. f4 c6 13. fxe5 Kd7 14. Be2 Ke8 15. c4 Nc7 16. Nc3 Be6 17. Bg5 Qd7 18. Rad1 Rc8 19. Bxe7 Qxe7 20. d5 Qc5 + 21. Kh1 cxd5 22. cxd5 Bd7 23. e6 Bb5 24. Qf4 Kd8 25. Bxb5 Nxb5 26. Nxb5 Qxb5 27. d6 1-0

Krasenkow's other important contribution is the so-called Groningen Attack in the English Opening ( discovered simultaneously with Vadim Zviagintsev ): 1. Nf3 Nf6 2. c4 e6 3. Nc3 Bb4 4. g4!

After 3. dxe5 Ng4, there is a battle over White's extra pawn on e5, which Black typically attacks with ... Nc6 and ( after ... Bc5 or ... Bb4 +) ... Qe7, while White often defends it with Bf4, Nf3, and sometimes Qd5.

For example in the Alekhine variation, after 1. d4 Nf6 2. c4 e5 3. dxe5 Ng4 4. e4 Nxe5 5. f4 Ng6 6. Nf3, the move 6 ... Bb4 + ( see diagram at right ) is good because White has no good reply apart from 7. Nc3.

Similarly, in the Rubinstein variation 3 ... Ng4 4. Bf4 with 4 ... Nc6 5. Nf3 Bb4 + 6. Nc3, after 6 ... Bxc3 + 7. bxc3 White is saddled with doubled pawns in c3 and c4 that limit the scope of his bishop pair.

The Bb4 is attacked but Black can play 7 ... Ngxe5 to get the gambitted pawn back, as 8. axb4 ??

His contributions to opening theory extend to reviving the Marshall Attack for Black in the Ruy Lopez ( 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. 0-0 Be7 6. Re1 b5 7. Bb3 0-0 8. c3 d5 ), developing the Leningrad Variation for White in the Nimzo-Indian Defence ( 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Bg5 ), the Spassky Variation on the Black side of the Nimzo – Indian, and the Closed Variation of the Sicilian Defence for White ( 1. e4 c5 2. Nc3 ).

Bb4 wins the queen ) axb6 18. Ra1 Re8 + 19. Kd2 Ne4 + 20. Kc2 Nxf2 21. Rg1 Bf5 +, which he considers winning for Black.

Today, the line arises quite often by transposition from the Black Knights Tango, e. g. 1. d4 Nf6 2. c4 Nc6 3. Nf3 e6 4. Nc3 Bb4 5. Qc2.

After 3. Nf3, Black usually plays 3 ... b6 ( the Queen's Indian Defence ) or 3 ... d5 ( leading to the Queen's Gambit Declined ), but can instead play 3 ... Bb4 +, the Bogo-Indian, named after Efim Bogoljubov.

If Black does not wish to play the Queen's Indian in response to 3. Nf3, alternatives include: 3 ... d5, transposing to the Queen's Gambit Declined ; 3 ... Bb4 +, the Bogo-Indian Defense ; and 3 ... c5, which typically leads to a Modern Benoni or a Symmetrical English.

However, it weakens the dark squares slightly, which Black can take advantage of by playing 5 ... Bb4 +.

Most often these defences consist of ... Nf6, ... e6, and ... d5 or ... Bb4 systemic responses by Black, or a Slav-like system consisting of ... c6 and ... d5, a direct King's Indian Defense setup with ... Nf6, ... g6, ... Bg7, ... 0-0, after which ... c5 and ... e5 are eschewed, or 1 ... f5, which usually transposes to a Dutch Defense once White plays d4.

1. Nf3 Nf6 2. c4 e6 3. Nc3 Bb4 4. g3 O-O 5. Bg2 c5 6. O-O Nc6 7. d4 cxd4 8. Nxd4 Qe7 9. Nc2 ( White allows Black to ruin his pawn structure, and soon sacrifices one of his weak c-pawns.

After 4. dxe5, Bauer concludes that " White stands a trifle better " but that " provided he plays accurately, Black doesn't have much to fear following 6. Bc4, by choosing any of the three valid replies, 6 ... Ke8, 6 ... Bb4, or 6 ... Be6.

Black has several choices here ; 3 ... Bc5 can transpose to the King's Gambit Declined after 4. d3 d6 5. f4 Nc6 6. Nf3 ; after 3 ... Nc6 4. d3, 4 ... Na5, 4 ... Bc5 or 4 ... d6 are all playable ; 3 ... Bb4 4. f4 Nxe4 5. Qh5 0-0 leads to wild but probably equal play, according to de Firmian in MCO-15.

Black cannot easily deviate from this line, since after 7 ... Nbd7 White continues 8. Qe2 e6 9. 0-0-0, aiming to launch a strong attack down the e and f-files, and if 9 ... Bb4 then 10. d5 !.

* Ideas for Black against the Catalan: 4 ... Bb4 +

After 3 ... e6, White can play 4. Nc3 Bb4 ( transposing to the Nimzo-Indian Defense ); 4. a3, when Black can either play 4 ... d5 ( reaching a kind of Queen's Gambit Declined or Ragozin System ), or 4 ... d6 preparing 5 ... e5 or even 5 ... g6 (" championed by Bologan ", according to Palliser ), reaching a sort of King's Indian Defense ; or 4. g3, when Black can transpose to the Catalan Opening with 4 ... d5, recommended by Palliser or 4 ... Bb4 +, preferred by Orlov, which transposes to a Nimzo-Indian after 5. Nc3, or to a Bogo-Indian Defense after 5. Bd2 or 5. Nbd2.

Black does best to immediately exchange the Nc3 with 6 ... Bxc3 + 7. bxc3 as otherwise White gets a small positional advantage simply by avoiding the doubled pawns ( see the section " Advantages of ... Bb4 +").

He does not like the strategy to retreat the Bb4 in d6 either, because they are too drawish.

The other gambit, 4 ... Nc6 5. Nf3 Bb4 + 6. Nbd2 f6 7. exf6 Qxf6, is much riskier, as Black weakens his kingside and does not open a diagonal for his Bc8.

Borik thinks 4. Qc2 is the move " that gives Black the most problems to solve ", but Lalic does not agree at all, stating that the reply " 4 ... Bb4 + followed by d7 – d5 ensures Black a rapid development and plenty of counterplay.

The other ideas, 6 ... Be7, which has the same drawback as after 5 e3 Be7, and 6 ... Bb4, have become sidelines in modern play.

Other move orders, such as 1. c4 e6 2. Nc3 Nf6 3. d4 Bb4, are also feasible.

( That alternative move order gives White other alternatives, including 6. Nxc6 bxc6 7. e5 Nd5 8. Ne4, intending c4, and the gambit 6. Be2 Bb4 7. 0-0!

In most variations Black has the opportunity to play Bb4 +, a move whose advisability depends on White's possible answers.

Bxd2 + 10. Qxd2 Qxe5, so he usually plays 9. e3 in order to protect the c4-pawn and defuse the mating threat, so that now Black is obliged to move his Bb4.

The move 11. Nb3 is not only useful to support the c4 – c5 push, but also to exchange the knight against Black's dark-squared bishop after a possible a2 – a3 forcing the retreat Bb4 – c5.

Lalic thinks both, considering 6 ... Bb4 + to be a bad move after 4 ... Nxe5 5. f4 Nec6 6. Nf3, but a good one after 4 ... Nxe5 5. f4 Nec6 6. Be3.

This move order enables White to avoid the critical main line of the Göring Gambit ( 1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. c3 dxc3 5. Nxc3 Bb4 ) by keeping open the option of meeting an early ... Bb4 by developing the king's knight to e2 rather than f3 and thus preventing Black from disrupting White's queenside pawn structure, as Alekhine did in his game against Pomar above.

Then Black has 6 ... Ne5 ( the Main line ), or 6 ... Bb4 ( Pinski's move ).