Queen's Gambit Declined Slav - 4.e3
1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. e3
White advances the queen's pawn to d4. Black pushes the queen's pawn to d5. White advances the c-pawn to c4.
Black moves the c-pawn to c6. White develops the knight to f3. Black develops the knight to f6.
White plays the king's pawn to e3.