White's challenged KB3(f3) Pawn exchanges,
removing White's newly doubled KP on K4(e4). Black develops his Queen to KR5(h4)
with check, to win White's KP (and if 5.P-Kt3?..QxKP+ch,
6..QxR).
White Black
1. P-K4 P-K3
2. P-Q4 P-Q4
3. P-KB3?! PxP
4. PxP Q-R5 ch