Chess Opening Theory/1. d4/1...Nf6/2. c4/2...c5/3. d5/3...b5/4. cxb5/4...a6

The standard Benko Gambit line. White has three common options available:

• 5. bxa6, accepting the gambit. Black then plays ...Bxa6, going into the classical Benko Gambit.
• 5. b6 allows Black to regain the pawn immediately via ...Qxb6, but in turn gives Black fewer open lines. This is a good line for players who don't wish to get involved in theoretical lines as White.
• 5. Nc3 is an interesting alternative where White prefers to just continue with development.

1. d4 Nf6 2. c4 c5 3. d5 b5 4. cxb5 a6

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

Wikipedia has related information at Benko Gambit.