2 testpositions from Chessbase. White to play and win!

[George Tsavdaris]

From here:
http://www.chessbase.com/newsdetail.asp?newsid=8837

White to play and win? How?
[d]1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1

The same here.
[d]2n3k1/p5p1/3p1pPP/1PpP1p2/2p2P2/1bP5/2R1P2r/R4K2 w - - 0 1

[ZirconiumX]

From here:
http://www.chessbase.com/newsdetail.asp?newsid=8837

White to play and win? How?
[d]1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1

Is this even solvable? Stockfish 130211 64bit - 8 threads - 2GB Hash:

Code: Select all

43    0.00    2377.9M    4:50.19 Qf4 exf4 Bc3+ Qg7 Ne8 Rb1+ Kh2 Rb2+ Kg1 Rb1+ Kh2

The same here.
[d]2n3k1/p5p1/3p1pPP/1PpP1p2/2p2P2/1bP5/2R1P2r/R4K2 w - - 0 1

Solved. Again Stockfish 130211 64bit - 8 threads - 2GB Hash:

Code: Select all

31    +4.92    94.6M    1:04.37 h7+ Kh8 Rxa7 Rh1+ Kf2 Nxa7 Ra2 Bxa2 b6 Ra1 Ke3 Rc1 Kd2 Ra1 e3 Rg1 bxa7 Rxg6 a8=Q+ Kxh7 Qa6  <snip>

Matthew:out

[Tennison]

From here:
http://www.chessbase.com/newsdetail.asp?newsid=8837

White to play and win? How?
[d]1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1

Is this even solvable? Stockfish 130211 64bit - 8 threads - 2GB Hash:

Code: Select all

43    0.00    2377.9M    4:50.19 Qf4 exf4 Bc3+ Qg7 Ne8 Rb1+ Kh2 Rb2+ Kg1 Rb1+ Kh2

Yes Matt It seems solvable :

1. Qf4 exf4 2. Bc3+ Qg7
3. Ne8 Rb1+ 4. Kg2 Rb2+
5. Kf1 Rb1+ 6. Ke2 Rb2+
7. Kd3 Rd2+ 8. Ke4 Re2+
9. Kd5 Rd2+ 10. Ke6 Re2+
11. Kd7 Rd2+ 12. Ke7 Re2+
13. Kd8 Rd2+ 14. Nd6 Rxd6+
15. Ke7 g5 16. Bxg7+ Kxg7
17. f8=Q+ Kg6 18. Kxd6 Nb5+
19. Ke5 Nd6 20. Qf6+ Kh5
21. Qg7 Nf7+ 22. Kf6 f3 23. Kxf7 f2
24. Qxh7# *

At least this will works ...

[Ajedrecista]

Hello Ben:

From here:
http://www.chessbase.com/newsdetail.asp?newsid=8837

White to play and win? How?
[d]1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1

Is this even solvable? Stockfish 130211 64bit - 8 threads - 2GB Hash:

Code: Select all

43    0.00    2377.9M    4:50.19 Qf4 exf4 Bc3+ Qg7 Ne8 Rb1+ Kh2 Rb2+ Kg1 Rb1+ Kh2

Yes Matt It seems solvable :

1. Qf4 exf4 2. Bc3+ Qg7
3. Ne8 Rb1+ 4. Kg2 Rb2+
5. Kf1 Rb1+ 6. Ke2 Rb2+
7. Kd3 Rd2+ 8. Ke4 Re2+
9. Kd5 Rd2+ 10. Ke6 Re2+
11. Kd7 Rd2+ 12. Ke7 Re2+
13. Kd8 Rd2+ 14. Nd6 Rxd6+
15. Ke7 g5 16. Bxg7+ Kxg7
17. f8=Q+ Kg6 18. Kxd6 Nb5+
19. Ke5 Nd6 20. Qf6+ Kh5
21. Qg7 Nf7+ 22. Kf6 f3 23. Kxf7 f2
24. Qxh7# *

At least this will works ...

Please try 4.- ..., f3+ in your mainline. It looks like a draw. I wonder about the solution.

Regards from Spain.

Ajedrecista.

[zullil]

From here:
http://www.chessbase.com/newsdetail.asp?newsid=8837

White to play and win? How?
[d]1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1

Is this even solvable? Stockfish 130211 64bit - 8 threads - 2GB Hash:

Code: Select all

43    0.00    2377.9M    4:50.19 Qf4 exf4 Bc3+ Qg7 Ne8 Rb1+ Kh2 Rb2+ Kg1 Rb1+ Kh2

Matthew:out

[d]4N2k/5Pqp/6p1/8/5p1p/n1B4P/8/1r5K w - - 4 4

Critter sees:

Code: Select all

27/44  00:01    2788K   2113K  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
28/47+ 00:02    4156K   1950K  +0.08 Kh2 Rb2+ Kg1 Rb1+ Kh2
28/49  01:03    6414K  101332  +0.21 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/52+ 03:29    9061K   43285  +0.29 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/54+ 05:42   17020K   49744  +0.42 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/61+ 05:48   39088K  112111  +0.61 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/61+ 06:01  183152K  507190  +0.90 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/67+ 06:28  491527K   1265K  +1.32 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/71+ 07:08  945284K   2204K  +1.96 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/75+ 08:06    1604M   3300K  +2.91 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7

[Tennison]

Hi Jesus,

Yes it seems the good way : open the f file for the rook ... (even if don't take in f3 you have to take on f1 later ...

Good look you have !!!

Better is Kh2 and not being too hurry with Kg2 ...

[zullil]

Code: Select all

29/75+ 09:35    2627M   4563K  +4.34 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7
29/80+ 10:53    3521M   5389K  +6.49 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nc4 Bxg7+ Kxg7 Ke7 Kh6 f8=Q+ Kh5 Qxf4
29/82+ 13:08    5152M   6535K  +9.70 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 Rd7+ Kxd7 Nb5 Bxg7+ Kxg7 Ke7 Kh6 f8=Q+ Kg5 Qf7 Na7 Qf6+ Kh5 Qxf4 g5 Qf7+ Kh6 Qf6+ Kh5 Qe6 Nc8+ Qxc8 Kh6 Qe6+ Kh5 Qf7+ Kh6 Kf6
29/82+ 18:22    9607M   8715K +14.52 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 g5 Bxg7+ Kxg7 f8=Q+ Kg6 Qf7+ Kh6 Kxd6 Nb5+ Ke7 Nc7 Qf5 Ne8 Qe6+ Kg7 Qf7+ Kh6 Qxe8 g4 Qc6+ Kh5 Qc5+ Kh6 Qd6+ Kh5 Qxf4 g3 Qf5+ Kh6 Qe6+ Kh5 Qg4+ Kh6 Qf4+ Kg6 Qxh4 h6 Qxg3+ Kh7 Kf6

[ernest]

Houdini 3 finds mate.

New game
4N2k/5Pqp/6p1/8/5p1p/n1B4P/8/1r5K w - - 0 1

Analysis by Houdini 3 w32 Nlm:

............
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kh2 Rb2+
= (0.00) Depth: 37/52 00:00:05 17853kN
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kh2 Rb2+
= (0.00) Depth: 38/52 00:00:06 22460kN
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kh2 Rb2+
= (0.00) Depth: 39/55 00:00:10 38016kN, tb=3
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kh2 Rb2+
= (0.00) Depth: 40/55 00:00:12 44383kN, tb=4
1.Kh2
= (0.06 !) Depth: 41/68 00:01:25 302mN, tb=89
1.Kh2
= (0.18 !) Depth: 41/68 00:01:54 408mN, tb=201
1.Kh2
+/= (0.45 !) Depth: 41/71 00:03:21 713mN, tb=338
1.Kh2
+- (1.47 !) Depth: 41/81 00:08:59 1849mN, tb=2488
1.Kh2
+- (4.40 !) Depth: 41/82 00:17:58 3233mN, tb=4406
1.Kh2
+- (12.72 !) Depth: 41/99 01:00:15 13824mN, tb=41092
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 41/99 01:03:51 14884mN, tb=47105
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 42/99 01:03:55 14904mN, tb=47356
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 43/99 01:04:00 14924mN, tb=47717
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 44/99 01:07:20 15915mN, tb=52583
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 45/99 01:07:44 16032mN, tb=54186
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 46/99 01:08:38 16293mN, tb=59398
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 47/99 01:18:04 19093mN, tb=70506
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 48/99 01:22:29 20407mN, tb=84689
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 49/99 01:25:44 21387mN, tb=96037
1.Kh2 Rb2+ 2.Kg1 Rb1+ 3.Kf2 Rb2+ 4.Kf1 Rb1+ 5.Ke2 Rb2+ 6.Kd3 Rd2+ 7.Ke4 Re2+ 8.Kd5 Rd2+ 9.Ke6 Re2+ 10.Kd7 Rd2+ 11.Ke7 Re2+ 12.Kd8 Rd2+ 13.Nd6 Rxd6+ 14.Ke7 h5 15.Bxg7+ Kxg7 16.f8Q+ Kh7 17.Kxd6 f3 18.Ke7 f2 19.Qxf2 Kh6 20.Qf7 Kg5 21.Qf6+ Kh6 22.Kf7 Kh7 23.Qg7#
+- (#23) Depth: 50/99 01:30:11 22683mN, tb=120974

[zullil]

Houdini 3 finds mate.

I assume Critter will too. I didn't bother to continue the search. Now I'm curious.

[EDIT] Yes.

Code: Select all

Critter v1.6a 64-bit, by Richard Vida
hardware POPCNT enabled
setoption name Hash value 4096
setboard 4N2k/5Pqp/6p1/8/5p1p/n1B4P/8/1r5K w - - 4 4
info string Opening book: "book.cbk" - 57853 entries [native]
info string GTB Init OK (5 piece set)
info string Using 8 thread(s), 4096 MB hash LP=off
go infinite
 2/ 3  00:00      249  249000 -12.75 Kg2 f3+ Kf2
 2/ 4  00:00      362  362000 -12.21 Kh2 Rb2+ Bxb2 Qxb2+ Kg1
 3/ 5  00:00      434  217000 -12.21 Kh2 Rb2+ Bxb2 Qxb2+ Kg1
 4/ 8  00:00      725  241666  -7.66 Kh2 Rb2+ Kg1 Rg2+ Kxg2
 5/ 9  00:00     1435  287000  -7.10 Kh2 Rb2+ Kg1 Rg2+ Kxg2 f3+ Kf2
 6/10  00:00     1657  331400  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
 7/10  00:00     1873  374600  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
 8/10  00:00     2078  415600  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
 9/10  00:00     2324  387333  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
10/10  00:00     2745  392142  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
11/12  00:00     3296  412000  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
12/16  00:00     4184  418400  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
13/16  00:00     5370  447500  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
14/17  00:00     7698  481125  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
15/17  00:00     9889  549388  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
16/17  00:00    11640  582000  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
17/22  00:00    18203  650107  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
18/22  00:00    24558  663729  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
19/29  00:00    37127  742540  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
20/29  00:00    49689  801435  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
21/31  00:00    77104  907105  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
22/31  00:00   103853  970588  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
23/38  00:00   181701   1128K  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
24/38  00:00   274882   1272K  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
25/38  00:00   452163   1453K  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
26/38  00:00   665116   1550K  +0.00 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/46+ 00:01    2268K   2060K  +0.08 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/46+ 00:01    2747K   2219K  +0.21 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/46+ 00:01    3450K   2383K  +0.40 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/49+ 00:02    5658K   2801K  +0.69 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/57+ 00:05   39524K   6589K  +1.11 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/63+ 00:13  119296K   8982K  +1.75 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/65+ 00:24  242366K   9959K  +2.70 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/65+ 00:42  439543K  10313K  +4.13 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/74+ 00:59  618942K  10384K  +6.28 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/74+ 01:28  946034K  10683K  +9.49 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/78+ 02:50    2065M  12146K +14.31 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/80+ 07:50    6802M  14451K +21.54 Kh2 Rb2+ Kg1 Rb1+ Kh2
27/84  08:46    7541M  14322K   +M23 Kh2 Rb2+ Kg1 Rb1+ Kf2 Rb2+ Kf1 Rb1+ Ke2 Rb2+ Kd3 Rd2+ Ke4 Re2+ Kd5 Rd2+ Ke6 Re2+ Kd7 Rd2+ Ke7 Re2+ Kd8 Rd2+ Nd6 Rxd6+ Ke7 g5 Bxg7+ Kxg7 f8=Q+ Kg6 Kxd6 Nb5+ Ke7 Nd6 Kxd6 g4 Ke5 h5 Qg8+ Kh6 Kf6 gxh3 Qg6#

[ernest]

Now I'm curious.

Still with Houdini 3.

Starting from the Mate position:

[Event "?"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "New game"]
[Black "?"]
[Result "*"]
[SetUp "1"]
[FEN "1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1"]
[PlyCount "10"]

1. Qf4 exf4 2. Bc3+ Qg7 3. Ne8 Rb1+ 4. Kh2 Rb2+ 5. Kg1 Rb1+ *

[d]4N2k/5Pqp/6p1/8/5p1p/n1B4P/8/1r4K1 w - - 0 1

where I get a Mate in 21

6.Kf2 Rb2+ 7.Kf1 Rb1+ 8.Ke2 Rb2+ 9.Kd3 Rd2+ 10.Ke4 Re2+ 11.Kd5 Rd2+ 12.Ke6 Re2+ 13.Kd7 Rd2+ 14.Ke7 Re2+ 15.Kd8 Rd2+ 16.Nd6 Rxd6+ 17.Ke7 h5 18.Bxg7+ Kxg7 19.f8Q+ Kh7 20.Kxd6 f3 21.Ke7 f2 22.Qxf2 Kh6 23.Qf4+ g5 24.Qf7 g4 25.Kf6 gxh3 26.Qg6#
+- (#21) Depth: 41/82 00:23:50 5960mN, tb=11811

...and backtracking (keeping the hash),
all is fine until

[Event "?"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "New game"]
[Black "?"]
[Result "*"]
[SetUp "1"]
[FEN "1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1"]
[PlyCount "10"]

1. Qf4 exf4 *

[d]1r3q1k/2N2P1p/6p1/8/5p1p/n6P/3B4/7K w - - 0 2

which is (accordingly) Mate in 25

2.Bc3+ Qg7 3.Ne8 Rb1+ 4.Kh2 Rb2+ 5.Kg1 Rb1+ 6.Kf2 Rb2+
+- (#25) Depth: 45/49 00:31:46 9670mN, tb=36004

But backtracking again, Houdini gives the defense 1.Qf4 h6 (instead of 1. Qf4 exf4 ) and Houdini no longer sees Mate, even after many hours

[d]1r3q1k/2N2P1p/6pQ/4p3/7p/n6P/3B4/7K w - - 0 1

1.Qf4 h6 2.Qxh6+ Qxh6 3.Bxh6 Rb1+ 4.Kg2 Rb2+ 5.Kf3 e4+ 6.Kxe4 Rf2 7.f8Q+ Rxf8 8.Bxf8 Nc4 9.Kd5 Nb2 10.Ke6 Kg8 11.Ke7 Nd3 12.Nd5 Ne5 13.Bh6 Kh7 14.Bg5 Kg8 15.Kf6 Nd7+ 16.Kxg6 Ne5+ 17.Kf5 Nf3 18.Nf4 Nd4+ 19.Kf6 Nf3 20.Ne6 Ng1 21.Bh6 Nxh3
+- (7.71) Depth: 36/92 01:22:15 18879mN, tb=33006
1.Qf4 h6
+- (7.39 --) Depth: 37/92 02:17:45 32531mN, tb=60009
1.Qf4 h6
+- (6.76 --) Depth: 37/97 21:40:33 314425mN, tb=416438