Queen's Gambit Accepted - classical variation - 6.O-O
1. d4 d5 2. c4 dxc4 3. Nf3 Nf6 4. e3 e6 5. Bxc4 c5 6. O-O
White plays the queen's pawn to d4. Black plays the queen's pawn to d5. White advances the c-pawn to c4.
Black captures on c4 with the queen's pawn. White develops the knight to f3. Black develops the knight to f6.
White pushes the king's pawn to e3. Black pushes the king's pawn to e6. White develops the light-squared bishop to c4.
Black advances the c-pawn to c5. White castles kingside.