Nimzo-Indian Defense: St. Petersburg Variation

The Nimzo-Indian Defense: St. Petersburg Variation is a chess opening classified under ECO code E43 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 9 moves: 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. Nf3 b6 5. e3 Ne4 6. Qc2 Bb7 7. Bd3 Bxc3+ 8. bxc3 f5 9. O-O. The resulting position leaves black to move.