second pawn after 6...Bg4 7.h3 Bxf3 8.Qxf3 Qxd4, leading to sharp complications, though Black can transpose back to the Classical Variation of the Teichmann Defence with 8...e6, since White's only good response is 9.Be3. Black can prevent this 6.Bd3 possibility by using O'Kelly's move order 4...c6. Ryder Gambit: 5.Qxf3 Alternatively, White can offer a second pawn with 5.Qxf3. Gary Lane argued in 2000 that White has serious problems proving enough compensation for the sacrificed pawns after 5... Qxd4 6. Be3 Qg4 7.Qf2 e5. Black can also decline the pawn with 5...c6 or 5...e6, holding the position. The Halosar Trap (named after Hermann Halosar) follows after 6... Qb4 7.0-0-0 Bg4? 8.Nb5! threatening mate with 9.Nxc7#. The black queen cannot capture the knight because 8...Qxb5 9.Bxb5+ is check, gaining time for the white queen to escape the threat from the bishop. The line continues 8...Na6 9. Qxb7 Qe4 (Black lost in Diemer–Halosar, Baden-Baden 1934, after 9...Rc8 10.Qxa6) 10. Qxa6 Qxe3+ (Worse is 10...Bxd1 11.Kxd1 Rd8+ 12.Bd2 and White is winning, for example 12...Ng4 13.Nxc7+ Kd7 14.Qxa7) 11. Kb1 Qc5 12. Nf3. Burgess wrote that "Although White has some advantage, Black has avoided instant loss". Fourth-move alternatives for Black O'Kelly Defence: 4...c6 Many sources recommend the O'Kelly Defence as a means of transposing to the Ziegler Defence while cutting out White's 6.Bd3 possibility, since White has nothing better than 5.Bc4, when 5...exf3 6.Nxf3 Bf5 transposes directly to the 6.Bc4 Bf5 variation of the Ziegler Defence. Alternatively, 5.Nxe4 is likely to land White in an inferior version of the Fantasy Variation of the Caro–Kann Defence, with equality at best in positions that may not attract Blackmar–Diemer players, 5.fxe4 e5! is good for Black and other bishop moves allow Black to achieve superior versions of standard Blackmar–Diemer Gambit variations. 4...c6 also has some independent value, for example Evgeny Bareev used the continuation 5.f3 b5!? in a game against Nigel Short, achieving a superior position after 6.Bb3 Be6 7.fxe4 b4 8.Nce2 Nxe4, but 8.Na4!? improves for White and may give sufficient compensation for the pawn. Black can also try 5...Bf5, when White must play accurately to prove enough compensation, but probably obtains sufficient play after 6.g4 Bg6 7.g5 Nd5 8.fxe4 Nxc3 9.bxc3. Vienna Defence: 4...Bf5 The Vienna Defence was recommended by Matthias Wahls in his book Modernes Skandinavisch, where he saw it as a refutation of the Blackmar–Diemer Gambit. White can play for compensation for a