Queen's Gambit Declined: Semi-Slav, Koomen Variation

The Queen's Gambit Declined: Semi-Slav, Koomen Variation is a chess opening classified under ECO code D31 in the Closed & Semi-Closed Games family, arising from 1.d4 d5, including the Queen's Gambit, Slav Defense, and related systems. It is reached after 7 moves: 1. d4 d5 2. c4 e6 3. Nc3 c6 4. Nf3 dxc4 5. e3 b5 6. a4 Bb4 7. Bd2 Qe7. The resulting position leaves white to move.