37. Nh5 is evidently the move here.

On 37.....gxh5 38. Rg1 mate

37.Nh5 (threat 38.Qg7#)

If 37...gxh5 38.Rg1#

There is no good defence after Nh5. Even heavy material sac (throw the queen with a check etc) doesn't stop mate for long

Okay so the solution is pretty straight-forward. Nothing more to see, nothing more to say, move along.

So let's rewind the game to a point where something interesting happens. And let's rewind our time machine back to the middle ages, when knights were encased in steel armour and Monty Python rode the land banging coconuts together. My Lords and Ladies, I present ye olde guide to storming a castle.

The field of battle stands thus, after whyte plays pawn to kynge's rook three (29. a3):

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Verily, the whyte army stands well. Observe, I pray, the might of the doubled whyte rooks that holdeth the d file in a steely grip. The blacke kynge hides in his tower, yet his keep is not so strong as once it was. His kynge's knight pawn has moved forwards one square (g6), in the fashion called by the Italians as being "in fianchetto". Yet the bishop that lived awhile in this tower (on g7) has been slain. Thus has the tower been weakened at his kynge's bishop third (f6) and kynge's rook third (h6).

The black kynge to his knyghte's second (29...Kg7). Blacke prepares for the retreat of his valiant knyghte, which is all alone at the edge of the field.

Then, the kynge's knyghte's pawn to his fourth. Black's knighte to his kynge's bishop third (30 g4 Nf6).

Whyte knyghte to kyng's bishop fifth! (31. Nf5!)

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A fine leap by the stallioned warrior! Howe'er blacke responds, whyte gains the attack. If the blacke kynge escapeth to his rook's house or his bishop's house, then mate swiftly follows. (31...Kh8 32. Qxf6+ Kg8 33. Qg7 or 31...Kf8 32. Qh6+ Kg8 33. Qg7#)

<Fast forward in our time machine to the position after 33...Qb5>

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The whyte army has advanced yet further into blacke's domaine. The whyte queen now holds the blacke tower in a mighty grip from her station at king's bishop's sixth (f6). The kynge's knight file stands half open, ready for a rook to join in the attack from the kynge's knyght's house (g1).

Now the whyte rook moves forwards one square to the queen's seventh (34. Rd7). If unattended, the whyte queen will next capture the bishop pawn, utter the cry of check and then proceed to checkmate along the seventh.

The blacke rook defendeth from the bishop's house (34... Rf8). Yea, this prevents the doom of checkmate, but it seals the black kynge in to his keep where he will surely perish.

Now whyte plays knyghte to bishops's fourth (35. Nf4). He prepares to give away his life, as if apparelled in a tabard of gules (wearing a red shirt).

My Lords and Ladies, the rest ye know. A pair of rooks are exchanged, but the battle is already won for whyte. Your humble scribe begs to point out that whyte's attacking force numbereth precisely three - one in a gules tabard to offer his life (the knyghte) and two to giveth checkmate - the queen and rook.

At one point in our tale, you might have thought that blacke's castle was a fine bastion, a mighty keep to rival Camelot itself. But this was merely a conjuror's illusion, a fancy constructed by Merlin to amuse the court. As we have seen, the castle was made of clay and straw, not rock and stone.

"Camelot!"

"Camelot!"

Black threatens 37... Qd2.

The dark squares around the black castle are weak and can be exploited immediately with 37.Nh5, trying 38.Qg7#:

A) 37... gxh5 38.Rg1#.

B) 37... Qd4 38.Qxd4 f6 (38... gxh5 39.Rg1#) 39.Qd7

B.1) 39... gxh5 40.Rg1+ Kh8 41.Qg7#.

B.2) 39... Rf7 40.Rc8+ Rf8 41.Qg7#.

White to play (37.?) "Easy"

Easy indeed, as White forces mate -

37. Nh5! gxh5

Or 37...Qd1+ delays the inevitable for one move, and the only other move to delay mate is 37...Qd4 38. Qxd4 f6, equally futile.

37 ... gxh5 38 Rg1#

The only defense for black is to throw in the queen and that is only delaying his inevitable doom.

37 ... Qd4
38 Qxd4 f6
39 fxg6 hxg6
40 Nxf6+ ...

40 ... Kh8 41 Nh5+ Rf6 42 Qxf6 Kg8/Kh7 43 Qg7#

40 ... Kf7 41 Rc7+ Ke6 42 Ng4 with mate next move as Qf6#, Qd7# and Qe5# are all available depending on black's response

Too bad the game-result did not allow for threats of the black king that white kings father smelt of elderberries :P

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Rybka 3:

R Vera vs J Becerra-Rivero

Difficulty: Easy

White is a pawn up. Despites how it looks, the white king is more safer than black king, because of the agressive position of white pieces. Trying to take advantage of that, I found the winning move. (Unfortunately, it took me more than I expected... 20 minutes! But I've just woken up :)).

37. Nh5!!

Threatening mate on g7. Its definitely unstoppable. The only try would be to remove the guard, by taking the knight

like this: 37 ... gxh5 38 Rg1# (But then the rook delivers the mate)

Wow, 26 ... Bd5! is so perfect, would stop everything up.

Black has a choice here. 37...Resigns or 37...Qd4 hoping for the uber-arrogant 38 e5?? which does indeed force mate - but perhaps not quite in the way White would have wished. After 38 Qxd4, Resigns is perfectly in order.