411 REFERENCE · Wikibooks
Chess Opening Theory/1. d4/1...Nf6/2. c4/2...c5/3. d5/3...b5/4. cxb5
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Benko gambit Benko gambit A57 4...a6
4. cxb5
White accepts the initial pawn.
The "real" gambit now follows with 4...a6, where White can take another pawn but Black can only recover one. In exchange for being a pawn down, Black hopes to capitalise on the open a- and b-files and a good structure in the form of a single large pawn island. 4...a6 is essentially the only move.
Note that 4...Qa5+? does not recover the pawn as 5. Nc3 interposes check and defends b5.
Theory table
.
1. d4 Nf6 2. c4 c5 3. d5 b5 4. cxb5
4
5
6
7
...a6
bxa6Bxa6
Nc3d6
Nf3g6
References
Benko Gambit