johnlspouge: Saturday (Very Difficult): White to play and win
Material: Down a P, with N for B. The White Bc2 pins Pf5 to Kh7. The Rg1 has an open file next to Kh7, and Rh1 is on the same file as Kh7. The Black Qf8 defends Be7, Rf6, and Ph6; the Black Rf3, Pe6, Pf5, and Ph6. The Pf5 and Ph6 are natural targets for a White attack. The Black Nd7 blocks development of Black's Ra8 and Bc8: without a specific reason, White should avoid exchanging it for Ne5.
Candidates (23.): Ng4, Nd5, d5, h5, Nb5, Rg5, Ne4
23.Ne4 (threatening Nxf6+, winning the exchange)
Because of the Ne5, Black cannot decline the sacrifice of Ne4 without losing the exchange.
Black must interpose 24…Rf5, or be down at least the exchange, because
24…Kh8 25.Ng6+ (threatening 26.Nxf8+)
26…Rxg6 26.Qxf8+ Bxf8 27.Rxg6 (threatening 28.Rhg1 29.Rg8#).
Defenses based on moves of Kh8 and Ph6 are too slow. Because the White Pd4 prevents Nd7 from blocking the Bc2 on the b1-h7 diagonal at d3, Nd7 must defend g8 from f6. The only three defenses preventing 29.Rg8#, other than those already mentioned, are therefore
(1) 27…Nf6 Rxf6
(2) 27…Bg7 28.Rhg1 Nf6 29.Rxg7
(3) 27…Be7 28.Rhg1 Nf6 29.Rxh6 Nh7 30.Rxh7#
If Black does interpose 24…Rf5, however,
24…Rf5 25.Bxf5 exf5
[25...Qxf5 26.Qg3 27.Qf8 Qg6+ 28.Kh8 Nf7+ wins Qf8]
26.Ng6 Q moves 27.Nxe7
Black is down the exchange if he does not recapture, so
27…Qxe7 28.Qxf5+ Kh8 29.Rg6 (threatening 29.Rxh6+ and 29.Rhg1)
Black has two possible defenses: (1) 29…Qf8 and (2) 29…Nf8.
(1) 29…Qf8 30.Qe6 (threatening 31.Qg8# or 31.Rxh6+ 32.Rhg1+)
30...Nf6 31.Qxf6+, and Black is down the exchange.
(2) 29…Nf8 30.Rxh6+ Nh7 31.Qg5, with several threats:
32.Qxe7, 32.Qe5+, 32.Qe8+, 32.Rhg1 and the maneuver Rh1-g1-g5-h5,
winning the Nh7. Black is down the exchange again.
Time to peek. Interesting. I preferred 24.Qxe4+ at first, because it nails Rf5 down with the mate threat. Because I did not find 27.Re1, I could not justify the move 23.Ne4. I will have the computer look at 24.Bxe4+. Time to check the kibitzing.
<dzechiel> said it very nicely: 23.Ne4 has to be the right move, because it activates Nc3, the only piece not directly attacking the Black K-side. It took me some time to see the right candidate, but I <can> be taught: it is the same motif as Wednesday's puzzle, Quinteros vs Christiansen, 1981, and even the same move (Ne4). The pin on the Pf5 degrades Pf5's protection of e4, enabling the N to move <onto> the diagonal of the pin.