411 REFERENCE · Wikibooks
Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nc3/3...Nf6/4. Nf3/4...e6/5. e3/5...Nbd7/6. Bd3
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Semi-Slav defence D46-D49 Semi-Slav
6. Bd3
White intends to enter the Meran variation. However, Black gets the final say in this matter.
After /6...dxc4/ Black has officially entered the Meran variation, forcing White to move the bishop again to recapture the pawn.
If Black doesn't want to play the theoretical Meran, they can avoid it with /6...Bd6/.
Theory table
Meran variation 6...dxc4 7. Bxc4 b5 Chigorin defence 6...Bd6
References
Semi-Slav Defence