Trap in the Queens Gambit Declined, Exchange Variation

This position arises after the moves: d4 d5 c4 e6 Nc3 Nf6 cxd5 exd5 Bg5 Nbd7. This is a well known trap, and the the d5 pawn is not hanging, as it seems to be. If the knight captures on d5 (Nxd5), then black is winning a piece. The next moves will be: .....Nxd5 Bxd8 Bb4+ Qd2 Bxd2+ Kxd2 Kxd8. Black is now in a winning position.

The full variation for your reference is: 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5 5.Bg5 Nbd7 6.Nxd5 Nxd5 7.Bxd8 Bb4+ 8.Qd2 Bxd2+ 9.Kxd2 Kxd8. +-