Queen's Gambit Declined Semi Slav . . .

Marshall Gambit where white offers a pawn for a strong attack on the dark squares.

Offering the d4 pawn...

Black accepts the pawn...

White takes the bishop and begins to bring dark squares in the black position under his control.

Black takes the knight with check to regain the piece...

White blocks the check with the Bishop offering the g2 pawn. If he wants to limit the gambit to one pawn then Ne2 is possible here.

Theory books will give lines to prove that taking the g2 pawn leads to very difficult positions for black. Common sense will say that with the Queen out and vulnerable and the dark squares under threat Black has no business taking any further pawns. I first came across this move when it was played against me in a congress a few years ago. Although it reduces by 100% the squares available to the light squared bishop it supports a push of the c pawn or e pawn to the fifth rank, blocks the action of the White Queen on d8 and also should that Q go to d6, prevents mate on f8. Theory smiles on moves like Na6 or c5...

Develops and blocks the line to g2.

Counters on the dark squares with this pawn advance supported by the knight.