or be prepared to sacrifice a pawn with either 4...Bd7 or 4...Nf6. 4...Bd7, the Caro Variation, an unconvincing variation according to Euwe after 5.exd5 Nd4 6.Qd1 Nxf3 7.Qxf3 Black has gambited a pawn with an unclear position. 4...Qd6, protecting e5 without weakening the pawn structure. Batsford Chess Openings 2 gives the move an exclamation mark but does not mention the reply 5.d4, the main move in the later Nunn's Chess Openings. 4...Nf6, the Leonhardt Variation. White can now gain material with 5.Nxe5, with theory giving 5...Bd6 6.Nxc6 bxc6 7.d3 0-0 8.Be2 Re8 where Black has compensation for the pawn. 4...f6, the Steinitz Variation, protecting the central e5-pawn is considered and best, but unnatural because it deprives the black knight of f6. The line can continue 5.Bb5 Nge7 6.exd5 Qxd5 with either 7.d4 Bd7 or 7.0-0 Bd7 and an equal position. 3...f5, the Ponziani Countergambit, is an aggressive Black response originally suggested by the 18th-century Italian writer, Ponziani. In 1951, Boris Spassky chose this countergambit against Yakov Estrin. The countergambit is considered better for White after 4.d4 fxe4 5.Nxe5 Qf6 6.Ng4 Qg6 7.Bf4 or 5...Nf6 6.Bg5. 3...Nge7, the unusual Kmoch Variation, was advocated by Hans Kmoch. According to Reuben Fine, citing analysis by Kmoch, Black equalizes after 4.d4 exd4 5.Bc4 d5 6.exd5 Nxd5 7.0-0 Be7 8.Nxd4 Nxd4 9.cxd4 Be6. 3...d6 reinforces the e5-pawn and intends to show that c3 was unnecessary. It is considered passive, however, and does not present White with any problems. After 4.Bc4, Black's most common responses are 4...g6, 4...Be6, and 4...Bg4. Illustrative games Here is a quiet draw typical of the 3...Nf6 line: V. Medvedev (2365) vs. Charles Milgram (2375), ICCF 1991 1. e4 e5 2. Nf3 Nc6 3. c3 Nf6 4. d4 Nxe4 5. d5 Ne7 6. Nxe5 Ng6 7. Qd4 Qf6 8. Qxe4 Qxe5 9. Qxe5+ Nxe5 10. Nd2 d6 11. Nc4 Nxc4 12. Bxc4 Be7 13. 0-0 0-0 14. Re1 Bf6 15. Be3 Bd7 While this game was agreed drawn there are good winning chances for White in this type of endgame. The variation 1.e4 e5 2.Nf3 Nc6 3.c3 Nge7 has been attributed to Reti due to him having tried it against Tartakower and lost. Recent analysis gives White the edge, i.e. 1.e4 e5 2.Nf3 Nc6 3.c3 Nge7 4.Bc4 (immediately targeting f7) d5 5.exd5 Nxd5 and now either 6.0-0 or 6.Qb3 lead to a White advantage. Also playable for White is 4.Bb5 which transposes