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Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nc3/3...Nf6/4. Nf3/4...dxc4/5. e4
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Vienna variation D37 Vienna variation
5. e4
White takes up the center and opens up the light-squared bishop to recapture the pawn on c4.
Black can choose to go into the sharp mainline with 5...Bb4 or to hang onto the pawn a little longer with 5...b5.
Theory table
5...Bb4 5...b5
References
See also