Queen's Gambit Declined Slav - Steiner variation
1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 dxc4 5. a4 Bg4
White moves the queen's pawn to d4. Black moves the queen's pawn to d5. White plays the c-pawn to c4.
Black plays the c-pawn to c6. White develops the knight to f3. Black develops the knight to f6.
White moves the knight to c3. Black captures on c4 with the queen's pawn. White moves the a-pawn to a4.
Black develops the light-squared bishop to g4.