Nimzo-Indian Defense: Classical Variation, Keres Defense

The Nimzo-Indian Defense: Classical Variation, Keres Defense is a chess opening classified under ECO code E32 in the Indian Defences family, where Black responds to 1.d4 with 1...Nf6, including the Nimzo-Indian, Queen's Indian, and King's Indian. It is reached after 6 moves: 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Qc2 O-O 5. a3 Bxc3+ 6. Qxc3 b6. The resulting position leaves white to move.