Classical Variation, Petursson Variation

The Petursson Variation departs from the main Carlsbad line by playing 10...Re8 at once instead of the customary 10...h6. Black does not question the g5-bishop. The rook goes straight to the half-open e-file, where it defends the e7-bishop and leaves the kingside pawns unmoved. The cost is that White's bishop keeps its pressure on the f6-knight, which guards d5, and can still choose its square later. The isolated d-pawn structure of the parent line remains.