A popular system, White doesn't mind the exchange of the bishop for the knight on c3 and even provokes it.
1. c2c4  1... e7e6  2. b1c3  2... d7d5  3. d2d4  3... f8b4 An interesting order of moves, usually taking the game to a position usually arising from the Nimzo-Indian or the Ragozin Defense.