London System · Line 13 of 19
...Qb6 before c3: the poisoned pawn
vs 1...d5 2...c5 3...Nc6 4...Qb6
If you've played Nf3 before c3, ...Qb6 looks like it wins the b2 pawn. It doesn't. Nc3! leaves b2 as bait: if Black's queen takes it, Nb5 brings the knight to c7 and the queen runs out of room.
As always.
Pawn to d4.
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