White advanced his king's pawn to the centre in response to Black's weak
QKt move, and his freed KB attacked Black's doubled QBP. Black advances his QKtPawn but will have difficulty
keeping the gained pawn, and has lost the centre.
White Black
1. P-Q4 P-Q4
2. P-QB4 PxP
3. Kt-KB3 Kt-QB3?!
4. P-K4 P-QKt4