Good Morning: That is not necessarily true - it could just have easily been home preparation.

10 0-0
not
10 cxd5

I checked on the computer & it was only slightly down for white with his King nicely protected in the corner
with 4 pawns a knight & 2 bishops.
That's a reasonable start & still winnable.

10. cxd5 (10. O-O Bxc4 (♗a6xc4 d4xc5 b6xc5 ♖f1-e1 ♘b8-d7 ♖a1-b1 ♕d8-b6 b2-b4 ♖f8-c8 b4xc5 ♕b6xc5 ♗d2-e3) +0.50/17 79)

white down less than half a pawn - depth 17

But the computer follows the text move on 12 & gives a poor result for white in this game:

12.b5 Rxe2+ 13. Kf1 (13. Kf1 (♔e1-f1 ♕d8-e8 ♔f1-g1 ♗a6xb5 ♕a4-c2 ♘f6-e4 d4xc5 b6xc5) -2.91/18 65)

<12 ... Rxe2+>

White cannot accept the rook sacrifice...

13 Kxe2 Qe8+
14 Kd1 Bxb5 (Ne5/Be3/Kf1/Kd3 Bxb5+ )
15 Qb3/Qc2 Ba4

Giving up Pf2 is going to create massive longterm problems for white, so Kd1 is probably not a good idea 13 Kd1 Qe8 14 Rb1 Rxf2

<13 Kf1 Qe8>
<14 Rb1 Ne4>

The rook is still immune due to Nc3+ and white must try to stop Nc3, but white cannot...

<15 Be1 Rxe1+>

16 Rxe1 Bxb5+

16 Kxe1 Nc3+

<16 Nxe1 Nd2+>
<17 Kg1 Nxb1>

Black is threatening 18 ... Qxe1+ 19 Bf1 Nd2 , so white must try to gain control of the h1-a8 diagonal.

<18 Bxd5 Nc3>
<19 Qb3 Nxd5>
<20 Qxd5 ...>

click for larger view

White is hoping to gain control of the h1-a8 diagonal, but that is just not going to happen as the white's LSB is gone and white has an entry point on c3 where Nb8 and Qe8 are dominant.

<20 ... Bxb5>

White can take Ra8, but the gain will be short lived...

21 Qxa8 Bc3
22 Qxa7 Qxe1#

White threatens bxa6.

The black queen would be better placed on e8. Therefore, 12... Rxe2+:

A) 13.Kxe2 Qe8+ 14.Kd1 (else 14... Bxb5+ 15.Qxb5 Qxb5+ - + [Q+N+2P vs R+2B]) 14... Bxb5 15.Qb3(c2) (15.Re1 Bxa4+ wins) 15... Ba4 pins the queen - + [Q+N+2P vs R+2B].

B) 13.Kf1 Qe8

B.1) 14.Ne5 Rxd2 wins decisive material (15.bxa6 Qxa4).

B.2) 14.Be3 Bxb5 and the subsequent discovered check will win the queen.

B.3) 14.Rb1 Ne4

B.3.a) 15.Kxe2 Nc3+ and 16... Nxa4 wins decisive material.

B.3.b) 15.Be1 Rxe1+ 16.Nxe1 (both 16.Kxe1 Nc3+ and 16.Rxe1 Bxb5+ win decisive material) 16... Nd2+ (16... Nc3 looks more complex) 17.Kg1 Nxb1 18.Bxd5 Nc3 seems to win decisive material.

C) 13.Kd1 Rxf2

C.1) 14.Rg1 Qe8 with the double threat Qe2+ and Bxb5 looks very good for Black.

click for larger view

Komodo-10.1-64bit:

<+0.38/33 10.dxc5 bxc5 11.Ne5> Bb7 12.0-0 Qe7 13.e3 dxc4 14.Nxc4 Bxg2 15.Kxg2 Qb7+ 16.f3 Nc6 17.b4 Nd7 18.Bc3 Nb6 19.Nxb6 axb6 20.Qb5 Na7 21.Qe2 cxb4 22.axb4 Rac8 23.Rfc1 Rfd8 24.e4 h6 25.h4 Qd7 26.Rd1 Qc7 27.Bb2 Rxd1 28.Rxd1 f6 29.Rc1 Qe7 30.Rxc8+ Nxc8

13 Kxe2 Qe8+
14 Kd1 Bxb5 (Ne5/Be3/Kf1/Kd3 Bxb5+ )
15 Qb3/Qc2 Ba4 >

[Part 1 of 2]

<<+> Not "insane*," just a little unbalanced <+>>

This puzzle didn't seem difficult to me, once I saw the great imbalance in the position: White's light-squared weakness and the fact that, if Black proceeds consistently, the pawn that now appears to stuff Black's bishop becomes a neon-glowing target.

The breakthrough:

<<+> 12. ...Rxe2+! >

Now White has to choose: take or don't. Let's examine both options respectively, on the principle that "the only way to refute a gambit is to accept it," and here Black is "gambiting" a whole rook.

1) <13. Kxe2, Qe8+!>

Suddenly, White finds himself under dire light-square pressure, noting among other painful things that his pawn on b5 is now pinned and inadequately defended.

And how is he going to get out of check?

1.1) If he stays where he is, he has to choose between 14. Ne5 and 14. Be3. Either way, Black wins queen for bishop with 14. ...Bxb5+.

1.2) He can't go to e3 or e1, and 14. Kf1 is met as above with 14. ...Bxb5+.

1.3) That leaves the main subvariation: <14. Kd1, Bxb5>.

Now White has a new question, and a new grim answer. Before, it was the king who had to step aside; now it is Her Highness' turn.

Again, though: Where will she go?

Her options are limited; <access denied> on a5, b4 and c4, she can choose between b3 and c2.

Either will be met with 15. ...Ba4 , pinning and winning the queen.

All this, because Black saw and consistently exploited White's light-square weakness.

So much for accepting the "gambit," which leaves him with rook and bishop for queen and pawn in an inferior position. White must be more circumspect than that.

2) If we're not going to take the rook, we have two ways to decline it.

2.1) <13. Kd1, Qe8>

Black is still being consistent. He pins and pressures the b-pawn, and he defends his rook on e2 (both of which happen to be light squares).

White faces the other side of that coin. His pawn is pinned, so he can't take the annoying bishop without losing his queen — in the best case for two minor pieces with 14. Qxa6. And given his queen's lack of mobility, losing that b-pawn looks awfully discouraging, particularly coming with gain of tempo and full activation on the light squares. So, let's look at defending it.

2.1.1) There is one way to do this, and that is <14. Rb1!?...>

2.1.1.1) The obvious continuation is 14. ...Rxf2, but this can be met with 15. Re1, and suddenly it is Black who is on his heels. He must keep his queen on the a4-e8 diagonal, but 15. ...Qd7 is met with 16. Ne5! with complications favoring White.

[End part 1]

[Part 2 of 2]

2.1.1.2) A better move, to my mind, is <14. ...Ne4!>. (The rook is immune: 15. Kxe2?, Nc3++ wins the queen.)

Now Black threatens 15. ...Nxf2+ and 15. Be3? loses the queen to a knight fork, so there's only one way to defend: <15. Be1...>

2.1.1.2.1) But now this bishop is overburdened, and e1 is no longer available for the rook, so how about <15. ...Rxf2!>, when White can't take because of that pesky fork on c3.

Also, Black now threatens both a queen incursion on e2 with check and the simple capture of the undefended bishop on g2.

This forces <16. Rg1>, when Black wraps up with a combination: <16. ...Nc3+ 17. Bxc3, Qe2+ 18. Kc1, Qe3+ 19. Bd2...> (19. Nd2, Qxc3+ 20. Qc2, Qxd4 21. Qb2 [or 21. bxa6, Rxd2!] Qxb2 22. Rxb2, Bb7 ) <19. ...Rxd2! 20. Nxd2▢, Qxg1+ 21. Bf1...> (or 21. Kc2, Qxg2 22. bxa6, Qe2 ), <Bb7 >.

There are still moves to be made, but there is no reason why Black should not be able to win with his three-pawn advantage and safer king.

2.2) <13. Kf1, Qe8...>

Here White intends to maintain the defense of his f-pawn. But this involves dangers of its own.

His first problem is how to keep hold of his light squares, the key to them being the pawn on b5. We've already seen what happens if he allows them to be overrun.

2.2.1) As in the previous line, we begin with the defense of this pawn with <14. Rb1...>.

But dangers set in immediately with <14. ...Ne4!>.

2.2.1.1) As in line 2.1 above, the rook is immune because of <15. Kxe2, Nc3++ 16. Kf1, Bxb5+ 17. Qxb5, Nxb5 >.

This means something must be done about the threat of ...Nxd2, not to mention ...Rxf2+. And if the bishop leaves the a5-e1 diagonal, there is also ...Nc3.

2.2.1.2) The most consistent reply is <15. Be1...>, but this is a gossamer defense immediately torn asunder by <15. ...Rxe1+!>, and how is White to continue?

2.2.1.2.1) <16. Kxe1, Nc3+ >

2.2.1.2.2) <16. Nxe1, Nxd2+ 17. Kg1, Nxb1 >

2.2.1.2.3) <16. Rxe1, Bxb5+ >

White's only other alternative is to come to the aid of his bishop, at the cost of surrendering the b-pawn.

White has to do this with his queen; allowing 15. ...Bxb5 with his queen on a4 would be catastrophic.

2.2.1.3) The first and more active of two options is <15. Qd1, Bxb5 16. Kg1...> (not 16. Rxb5, Rxf2+ 17. Kg1, Qxb5 ) <16. ...Nxf2 17. Qc1, Nd3 >, when Black wins whether White takes the queen off the back rank or not.

2.2.1.3.1) <18. Qc3, Rxg2+ 19. Kxg2, Qe2+ 20. Kh3, Bd7+ > leaves White's king walking to his death.

2.2.1.3.2) <18. Qf1, Rxd2!> and Black wins a piece thanks to the threat of 19. Nxd2? (or 19. Rxb5?), Qe3+ with mate in one.

2.2.1.3.3) <18. Qd1, Ba4 19. Qf1, Rxd2! > transposes into a similar problem for White.

---

*Looking back over this long post, I find that the puzzle was a bit "insane" after all — but only in terms of volume of variations, not in theme. (Sufficient volume that I left this post half-composed and returned to complete it a day late.)

The *idea* for Black is very clear: White's light squares are weaker than they appear. If you exploit this weakness thematically, you will win.