Preparing a4-a5 with a majority attack on Black's vulnerable queenside.

1...a5?! 2.Ndb5 Be7 3.Bh6 , preparing Rd2 and Rad1, Black is in big trouble.

2...bxa5 3.Nb3! , followed by Nxa5 – Petrosian.

In order to exploit the new weakness on a5.

White later realized his positional advantage.

Softening up White's pawn majority and freeing the d5-square for the knight.

Preventing ...b5-b4, but also leaving the queenside structure in a bad shape.

3.Ne5 would be better.

After some consolidating moves Black is ready to fight for the initiative by ...Nbd5 or ...Nc4.

This loses a piece.