Picture 1. White to move and win in 3 moves.A rook-pawn on the 7th rank supported by its own King draws against a Queen if the enemy King can’t also join in the attack. The usual tactic of forcing the Black King to occupy the square in front of its pawn, so that Whit’s King gains a move to come closer, doesn’t work because of stalemate. But here the presence of a second Black pawn on g4 evokes another possibility. It allows White’s Queen to trap Black’s King for two moves, without fear of stalemate, as White’s g-pawn plays to g3 and g2. During the interim, White’s Queen slices through to unstoppable mate.
1. Qb3 g3
2. Qc2 g2
3. Qc1 mate
Picture 2. White wins with 3.Qc1.