Chess Opening Theory/1. d4/1...Nf6/2. c4/2...e6/3. Nc3/3...Bb4/4. Bg5

= Nimzo-Indian Defence, Leningrad Variation =

4. Bg5
White decides to match Black pin for pin, and the e4 square is once more a no man's land. More subtle is the fact that Black's knight no longer controls d5 either. For that reason, van der Sterren calls the d5 advance "the point but also the necessary consequence of 4. Bg5." Either 4...h6 5. Bh4 c5 6. d5 or 4...c5 5. d5 h6 6. Bh4 is almost always played.