Black's QP advanced to a classical pawn centre, freed
his QB and attacked White's light B and KP. White'sQB4(c4) Bishop under attack withdraws
to QKt3(b3) keeping pressure on Black's QP.
W-Alt.
White Black
1. P-K4 P-K4
2. B-B4 Kt-KB3
3. P-Q3 P-B3
4. Kt-KB3 P-Q4
5. B-Kt3