1. First and foremost, Re7: as a sacrifice that takes away an important defending piece: The Black Bishop is potentially protecting f6, g7 and h6 against a White attack.

2. The lounge Nf5 (After Re7: or in itself) is bringing one piece closer to the King.

3. The sacrifice Ng7: (After Nf5), perhaps followed by moves like Kg7: Qf6+ Kg8 and either Bh6 or Rf3, eyeing g3 with mate after Rfe8 and Bh6.

4. The move Bh6 (After Nf5 or in itself) with the pawn cover intact, threatening Bg7: (Or Ng7:). There could follow (at the Nf5-lines) h6: Nh6+ Kg7 (Kh8) Qf6#.

5. A mate of Knight and Bishop after Nf5 and a move like Bg5. Without the g7-pawn there is a mate like Nh6+ Kh8 Bf6#.

Let us begin with some tries:

I. 29. Bg5 f6 30. Nf5 e5: 31. Ne7+ Qe7:
(Kh8 32. Qf8: Rf8: Rf8:#) 32. Be7: Rf3: 33. Rf3: Re8 34. d6 Nc6 and Black is a pawn up with the strong paased pawns.

II. 29. Nf5

1. 29. .. Bf6 30. Nh6+

a. 30. ... Kh8 31. Rf5 threatening Rf6: f6: Qf6:# (motif) 31. ... h6: 32. Rf6: with a strong attack

b. 30. ... h6: 31. Qf6: (threatening 32. Bh6 and 33. Rg5#) 31. ... Qd6 32. Bh6: Qf6: 33. Rf6: and 34. Rg5# follows.

2. 29. ... Bc5 30. Bh6 with a strong attack, see 30. ... h6:? 31. Nh6:+ and 32. Qf6#

3. 29. ... Bd6 seems to hold, 30. Nh6+ h6: 31. Qf6 Be5: 32. Qe5: Qd6 and Black is a Rook up.

III. 29. Bh6 with threats like Bg7: Kg7: Re7: Qe7: Nf5+ forking King and Queen or Qg3 g6 winning at least an exchange.

1. 29. ... h6: 30. Nf5

a. 30. ... Bf6 31. Nh6:+ and 32. Qf6:#

b. 30. ... Bg5 31. h4 and the attack continues, but probably not strong enough to break through

2. 29. ... Bf6 30. Qf6: f6: 31. Rf6: Qg4 32. h3 Qh4 33. R1f5 with the threat of Nf3, but after 33. ... Qf6:! 34. Rf6: a5, Black is still winning.

IV. 29. Re7: Qe7:

1. 30. Nf5

a. 30. ... Qe8 (d7, c7, b7, a7, c5) and
now 31. Ng7: or even Bh6 should win right away (h6: Nh6:+ and Qf6#; else Bg7: next move, followed by Qg3 etc...)

b. 30. ... Qf6 31. Nh6+

b1. 31. ... Qh6: 32. Bh6: h6: 33. Qf6 with a winning attack because of the mate threat Rf3, Rg3#. 33. ... Rc8 34. h3 Rc7 (So that the f-Rook can move) 35. Rf3 Re8 36. Rg3 Kf8 and now Rg7, Rh7:, Rh8 should be enough, combined with a timely d6.

b2. 31. ... Kh8 32. Qf6: f6: 33. Bd4 should win, for instance 33. ... Kg7 34. Nf5+

b21. 34. ... Kh8 35. Bf6:+ Kg8 36. Nh6#

b22. 34. ... Kg8 35. Ne7+ Kg7 (Kh8 36. Bf6#) 36. Bf6:+ Kh6 37. Rf4 and 38. Rh4# follows.

So, let us review:

Not all of our motifs became visible during our analysis, but new, basic ones like the Nh6:+, Kg7, Qf6:# - sequence emerged. The final mate with Bishop and Knight working together to bring the King to the Rook was also noteworthy.

At the end, our main line:

Rxe7 is about as natural as a sacrifice gets, and Nxg7 with threats of Qf6 and Re3-g3 is a tactic that I already know very well. Combining the two ideas was not very difficult (for a Saturday).

Yesterday's puzzle had a large number of false leads, making finding the first move of the combination very difficult by comparison.

BTW, I didn't even consider 31...Nc2. Unless White was very low on time, I thought that probably the best move was to resign. 31...Nc2 does prolong the game by controlling the d4 square, but it doesn't matter.

Of course the Knight is untouchable, because what follows after its capture is 31...Kxg7 32. Qf6+ Kg8 33. Bd4 with a decisive dual mate threat (34. Qg7# or 34. Qh8#).

After 35.Nf5
14-ply (-15.67) 35...Ra8 36.Bg7 Qxf5 37.Rxf5 Rd6 38.Rg5 Rg6 39.Rxg6 and so on

After 35.Nh5
17-ply (-16.26) 35...Rd6 36.Nf6+ Rxf6 37.Rxf6 a5 38.Rf5 Re8 39.Rg5+ and so on

So as <Some call me Tim> pointed out, they're both easily winning moves, but from the silicon monster's point of view the played move still holds the edge.

For the record, with the suggested rebuttal to 35.Nh5, 35...f5?, Rybka sees a considerably greater advantage for White; after 36.Nf6+ a mate in 9 beginning 36...Rxf6 37.Qxf6 Rg7 38.Qd8+

40.Rc1

or

40.Rf3