White's dark Bishop on QKt2(b2) captures
Black's K4(e5) pawn, completing a pawn exchange. Black castles early on his king's side to bring his King's
Rook closer to the now half-open king's file.
White Black
1. P-QB4 Kt-KB3
2. P-QKt4 P-K4
3. B-Kt2 BxP
4. BxP 0-0