comment: A much riskier line than the traditional ways of playing the Queen's Gambit Accepted with Nf6-e6-c5. Black's idea is not to end up with an extra pawn, because that is impossible, but to change the pawn structure on the queenside.
context: 1. d2d4  1... d7d5  2. c2c4  2... d5c4  3. g1f3  3... a7a6  4. e2e3 