411 REFERENCE · Wikibooks
Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. e5/3...c5/4. c3/4...Nc6/5. Nf3/5...Qb6/6. a3/6...c4
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French Defence: Advance Variation Advance Variation C02
6...c4
Black stops White from expanding on the queenside with b2-b4 because of an en passant capture on b3. Furthermore, Black restricts White's f1 bishop range of movement.
Theory table
7. Nbd7
References
French Defence