411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...c6/2. d4/2...d5/3. e5/3...c5/4. dxc5/4...e6/5. Be3/5...Nh6/6. c3
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Caro-Kann Defence - Advance Variation, Botvinnik-Carls Defence
6. c3 · Caro-Kann Defence - Advance Variation, Botvinnik-Carls Defence
Black will likely swing the knight to f5, which was the point of 5... Nh6. 6. c3 allows the bishop to safely go to d4.
Theory table
6... Nf5
References
Caro-Kann
Opening Repertiore: The Caro-Kann. 2015. Jovanka Houska 9781781942109