1. Nd6 Bxd6

when 1. ..Rc8 is not really an option I think, due to 2. Nxf7! Kxf7 3. Ba2+ Ke7 4. e6 with a crushing attack.

2. e6!?

this really opens up the bishops to black's king. in case black doesn't take on e6, 3. exf7+ draws out the king just like in the note after 1. ..Rc8.

2. ..Rxe6
3. Rxe6 fxe6
4. Bxg6

i think white will respond with

27. exf7+ Kxf7
28. Nd6 winning.

Material even. K-side spatial advantage with Bs on adjacent long diagonals, Ns and Q mobile and centralized, R backing Pe5. Black has potential mating threats on a8-h1. Both Ks in some danger, but Black's more so. Black: Nd2 supported 1x(Q); Ng3 supported 2x(Q,Pf7), Re8 supported 0x. White: Pe5 supported 2x, threatened 3x. The position is so open that positionally the minor exchange is worth more than usual.

Candidate moves: Bxh6 (whoops, force of habit), Nf6+, e6, Nd6, Nd4.

Later candidates: Ba2||e4, Q+B battering ram

The key is probably opening the a1-h8 diagonal and getting rid of Bf8. 25.Nf6+ or e6 go nowhere, and the Nd6 lacks sufficient support. In the end, ...Nxe5 might do White a favor. The Re1 is a liability in some variations, because of ...Rxe1. Disrupting Black's mate threat looks attractive.

25.Nd4 Qd5 26.f4

This line feels right. White has fortified g2, centralized pieces, and tightened control of the center. The Black Q can be pushed off the a8-h1 diagonal. Time to peek.

Nope. I need to see why 25...Rxe6 was impossible.

<blummenstuhl: Sometimes things are so simple and you just don´t see it.>

Here's a breakout of the combo, verified with Fritz 8:

<25. e6!! Nb6>

White gets small but clear advantage(s) if Black captures the "sacrificed" pawn. However, against a strong player like GM Nunn those advantages are likely decisive. Here's what happens if Black grabs the pawn:

[25... Rxe6 26. Nd4 ;
25... fxe6 26. Neg5 hxg5 27. Bxg6 Re7 28. Qxg5 ;
25... Qxe6 26. Ng3 Nge5 27. Nxe5 Qd5 (27... Nxe5 28. Rxe5 Qxe5 29. Bxe5 Rxe5 30. Qd3 ) 28. Qxd5 Bxd5 29. f4 f6 30. Rd1 Nxe5 31. Rxd5 ]

<26. Bxg7! Nc4> This is best, as taking the poisoned piece loses immediately:

[26... Bxg7 27. exf7+ Kxf7 28. Nd6+ ;
26... Kxg7 27. Qd4+ Kg8 28. Nf6+ Kh8 29. Nxe8+ ]

<27. Qxh6! Rxe6>

The Bishop is still poison, as Black loses quickly after 27... Bxg7 28. Nf6+ Bxf6 (28... Kf8 29. Nh7+ Ke7 30. exf7+ Nce5 31. Qxg7 ) 29. exf7+ Kxf7 30. Bxg6+ Kg8 31. Qh7+ Kf8 32. Qf7#.

<28. Bxf8 Nxf8 29. Qg5+ Rg6 30. Qf4 Ne6 31. Nf6+> 1-0.

Although this was enough to convince Black to resign, a stronger move is the computer choice 31. Qh4! Nf8 [31... Rg7 32. Nf6+ Kf8 33. Qh8+ Ke7 34. Qxg7 ; 31... Kf8 32. Kh1 Kg8 (32... Rg8 33. Nf6 ) 33. Nf6+ Kg7 34. Nh5+ Kf8 35. Bxg6 fxg6 36. Qf6+ Ke8 37. Ng7+ Kd7 38. Nxe6 ] 32. Ng3 Qf6 33. Bxg6 Qxh4 34. Bxf7+ Kxf7 35. Nxh4 .

If Black had chosen to continue, he could have put up a bit of resistance with 31... Kg7 32. Nh5+ Kf8 33. Qb8+ Qc8 34. Qxc8+ Bxc8 35. Bxg6 fxg6 36. Nf6 Nxa3 37. Nd5 .However, even if he managed to visualize this line, I supsect Greenfeld figured with the exchange down against GM Nunn he didn't have a chance in the endgame.

<patzer2: <johnlspouge> <I need to see why 25...Rxe6 was impossible> Not impossible at all.>

That's very generous. I still have a neophyte's horror of the complexities in a Sunday puzzle. Over the board, I will need some more experience before I prefer e6 to Nd4.

Nunn and I were contemporary at the Oxford mathematics department. I recall recognizing him walking down the High Street, although he never knew me. Within the mathematics department, he was known as quite a strong chessplayer ;>)

Hi, <patzer2>. You can call me "John", although I insist on "Dr. Spouge" from my enemies :>) Given the several posts making passing reference to my title, however, I have realized that I can accept "Dr. John" as a pleasant and jocular familiarity from the people here.

No, I did the medical degree first and pithed myself thoroughly, to make the mathematics degree challenging (which it was). The two other MD-PhD mathematicians I have known did their mathematics degree first. I am nothing if not a committed masochist.

Getting a late start on today, but let's see if we can offer anything original.

At first glance the black king seems safe enough. But, compared with white, black's pieces are relatively uncoordinated. Black's rook is undefended should the e-file open somehow. The knight on d7 is only defended by the queen.

Black's last move was likely ...Ng6, probably coming from e7, otherwise you wonder why black wouldn't have capured the e-pawn.

Some candidate moves that come to mind are:

- 25 Nd4
- 25 Rc1
- 25 e6

In all the lines I'm looking at, pushing the e-pawn plays an important role. This makes me believe that 25 e6 might well be the key move.

I have, however, learned from past "insane" positions, that I am out of my depth here. And while I would love to spend an hour finding the winning line, it's not clear to me that I could find it even given that much time.

I’m not seeing the win after 28…Qc4.

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