Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. Nc3/3...dxe4

Black has taken White's e-pawn and denied them the classical two-pawn centre. By taking the pawn, Black frees up the space it controlled and creates new possibilities for their piece development.

4. Nxe4, recapturing the pawn is the natural and most common response, which usually leads to one of three main lines, 4...Bf5, the classical variation, 4...Nd7, the Karpov variation, or 4...Nf6 5. Nxf6+ exf6, the Tartakower variation.

White may choose to gambit the pawn with 4. f3 or 4. Bc4 for a development advantage. White doesn't receive full compensation for the pawn, but the lines can be sharp.

4. f3 is the Rasa-Studier gambit. White offers Black the f-pawn to remove the problematic e-pawn so that they can recapture it by developing a new piece, 4...exf3 5. Nxf3. This leads to positions resembling the Blackmar-Diemer gambit.

4. Bc4 is the Von Hennig gambit, though this comes with the same idea to play f3 and the two gambits usually converge after 4...Nf6 5. f3 exf3 6. Nxf3. If Black declines to take the f-pawn there are other original lines.

1. e4 c6 2. d4 d5 3. Nc3 dxe4

Wikipedia has related information at Caro-Kann.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.