411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...c6/2. Nc3/2...d5/3. Nf3/3...Bg4
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Caro-Kann Defence: Two Knights Attack B10
3...Bg4 · Caro-Kann Defence: Two Knights Attack
3...Bg4 frees Black's problematic dark-squared bishop. White's most common response, 4. h3, leads either to sharp lines with a lot of theory, or to Black giving White the bishop pair.
Theory table
4. h3 Bxf3 5. Qxf3 4. Be2 4. d4
Caro-Kann