Grünfeld Defense: Three Knights Variation, Petrosian System

The Grünfeld Defense: Three Knights Variation, Petrosian System is a chess opening classified under ECO code D91 in the Closed & Semi-Closed Games family, arising from 1.d4 d5, including the Queen's Gambit, Slav Defense, and related systems. It is reached after 5 moves: 1. d4 Nf6 2. c4 g6 3. Nc3 d5 4. Nf3 Bg7 5. Bg5. The resulting position leaves black to move.