Queen's Indian Defense: Kasparov-Petrosian Variation, Marco Defense

The Queen's Indian Defense: Kasparov-Petrosian Variation, Marco Defense is a chess opening classified under ECO code E12 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 5 moves: 1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. a3 Bb7 5. Nc3 Be7. The resulting position leaves white to move.