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The King's Indian Defense, Petrosian System

(In the King's Indian Defense, usually Black attacks on kingside, with f5-f4, closing down the centre and following by g5-h5, g4, trying to destroy the defense on kingside; and White has a counter play on queenside, with b4-c5, maybe cxd6, after cxd6 there will be a weakness in d6, White can try to attack here.)

1 d4-Nf6, 2 c4-g6, 3 Nc3-Bg7, 4 e4-d6, 5 Nf3-0-0, 6 Be2-e5; in that position, White can castle here, (which is one of the most common variations) after 7 0-0, Black plays Nc6, allows to d5 with a tempo, but after d5, Ne7 and here, in Black's kingside attack, the Night that is in the e7 square would be very useful.

In the Petrofina System, White plays d5 before the castle, not allowing to Nc6 and Ne7. So, Black has to find a place to the Night. Also, White threats b4, following c5. So in that position, obviously most common move is a5. a5 move prevents b4 and simultaneously allows to b8 Night to make a maneuver Na6 and Nc5. (Nd7 and Nc5 is also possible.)

7 d5-a5, 8 Bg5

In here, White should place his/here Bishops e3 and e2 squares and his/here Nights to d2 and c3 squares. That is the most ideal position for White pieces, but it is not that easy. Because, if White plays Be3 immediately, (Be3 was played against The King's Indian Master Garry Kasparov, and Kasparov played 8...Ng4, 9 Bg5-f6, 10 Bh4-Na6, 11 Nd2-h5 ... in the game, Kasparov forced the Bishop to go h2 square, and played on the Bishop nicely. For that reason, White plays Bg5, forcing Black to play h6, which would be good target for White.

8 ...h6, 9 Bh4-Na6, 10 0-0-Qe8

In here, Black could play Bd7 instead of Qe8, both two moves has a common idea, controlling the a4 square. I'll explain why this is important for Black, after a couples move. Now have look at the Bd7 move. 10 ...Bd7, 11 Nd2 (White is preparing for a queenside attack, after b4-c5 Night will jump to c4 square.)-Nc5, 12 b3; and here Black can go for Qe8-Nh7 and f5 idea, or Nfxe4. It looks crazy, 12 ...Nfxe4, 13 Bxd8-Nxc3, 14 Qe1 and Rfxd8. Yes, it looks like Black sacrificed his/here queen for two pieces, but after e4, the Bishop which is in g7 square will be a very strong Bishop, Black will be a good counter play against this exchange. And in that position, computer says that it is almost an equal position. (+0.3)

11 Nd2-Bd7

And here, the controlling a4 square is important for Black, because here White cannot play a3, with the idea of b4. Because if White plays a3, Black simply plays a4 and lock down everything for White, in queenside. So White have to play b3 first, than a3 and b4. And that will make slower White's attack.

12 b3-Nh7

Black prepares f5.

13 a3-h5

In that position Black can play f5, after exf5-gxf5 (Black can't take the Pawn with their Bishop, because if Black takes the Pawn with Bishop, Black will simply give e4 square (which is a very nice and useful square) to White, and that will be the end of attack.) Anyway, after gxf5-gxf5, White plays Bh5, and here, if Black wants to continue attack, Black has to give up their Rook, with Qc8. 15 Bh5-Qc8, 16 Be7-Re8, 17 Bxe8-Qxe8, 18 Bh4-e4, 19 Rc1-Nc5, 20 Rc2... and this position is fine for both sides.

Now, if we look at the h5 move, the threat is obvious: g5, Bg3 and h4. So, White should play f3 to put their Bishop to f2 square. And g1-a7 is a ver good diagonal for the Bishop, in attack and in defense.

14 f3-Bh6

Black is trying to put their Bishop to a nicer place, as you'll see.

15 Rb1-Be3+, 16 Kh1-Bc5

Now, Bishop is very active and Bishop prevents the b4 move, for now.

17 Qc1-f5, 18 exf5-gxf5, 19 Bf2 and Qg6.