Queen's Indian: 4.a3, the Petrosian is variation 6 of 6 in the Against the Nimzo-Indian and Queen's Indian course, a advanced opening course for White (ECO E12). It runs 25 moves and begins 1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. a3 Bb7 …. With a3 White stops the bishop check. After the trades on d5 and c3 White builds a big centre with pawns on c3, d4 and e4. The bishop on d3 aims at h7. In the lesson every move is explained on a board and then drilled; it is free.
Move by move
1. d4 – White takes the centre.
1... Nf6 – Black develops.
2. c4 – White gains space.
2... e6 – Black opens the bishop.
3. Nf3 – White develops the knight and avoids the Nimzo pin.
3... b6 – The Queen's Indian. The bishop goes to the long diagonal to watch e4.
4. a3 – The Petrosian. White stops the bishop check on b4.
4... Bb7 – Black develops the bishop to the long diagonal.
5. Nc3 – White develops and fights for e4.
5... d5 – Black takes the centre.
6. cxd5 – White clears the centre.
6... Nxd5 – Black takes back with the knight.
7. Qc2 – The queen fights for e4 and gets ready to push the e-pawn.
7... Be7 – Black develops the bishop.
8. e4 – White grabs the centre with tempo on the d5 knight.
8... Nxc3 – Black trades.
The lesson goes on for 9 more moves, each with its explanation.
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