The Petrosian System (also known as the Taimanov Variation) is a sideline white could choose to fight the Grünfeld Defense.
It’s not as good as the Exchange variation, both according to the engines and to theory. It allows black to have a simpler game in which he doesn’t have to prove compensation for white’s big center.
It starts after the moves Nf3 and Bg5 for white. After Nf3 (…Bg7), white could still choose the Russian Variation, which is more principled, but if he continues with Bg5, getting the bishop to a very active square in black’s position, that is the Petrosian system
The downside of the move is twofold. Firstly, the c4 pawn can be taken. In fact, in the most common sideline for black, he takes the pawn and holds on to it! It’s almost a clean pawn up. The second weakness is the fact that the bishop can be used as a tempo gain.
In the main line for black, black plays Ne4, attacking the bishop. That either forces it to move for the second time, or forces white to give up his dark squared bishop, the counterpart of the powerful g7 bishop which is the soul of black’s position. In either case, black should be equal already. It’s not easy to play black because white often starts a menacing attack very early on, but if black manages to defend, he is going to be slightly better.
I would advise you to play the Petrosian system if you are looking for a sharp, imbalanced weapon against the Grünfeld Defense. Otherwise, play the main lines. They are better for white.
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