English - symmetrical - three knights system
1. c4 c5 2. Nc3 Nf6 3. Nf3 d5 4. cxd5 Nxd5
White pushes the c-pawn to c4. Black moves the c-pawn to c5. White develops the knight to c3.
Black develops the knight to f6. White jumps the knight to f3. Black moves the queen's pawn to d5.
White captures on d5 with the c-pawn. Black captures with the knight on d5.