Advice on how to solve a difficult position / advice on Chest

[fkarger]

Recently I tried to analyze the following position:

[d] 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

Source: HHdbVI, Behting=C (+0341.02g5c1), Rigasche Rundschau 1905

According to the source the solution is 1.Kf6.

I would like to solve the following questions:
1) Does Kf6 win?
2) Does White win at all?
3) If Kf6 wins is there an alternative win?

So far I was not able to prove a win.
I assume that it is possible to configure a mate finder like Chest that it
can try to find the shortest win (in reasonable time).

So my questions for the honorable audience are:
A) How would you approach this with chess engines?
B) Which engines would you recommend?
C) How to use Chest for this kind of a problem?

Best regards

[fkarger]

UPDATE

I managed to answer

1) Does Kf6 win? (yes)
and
2) Does White win at all? (yes)

by using Sting 23 and slowly stepping back from the winning line (according to the source) which is:

1. Kf6 $1 Kc2 2. Ke7 Kd3 (2... Kc3 3. Kd7 Kd3 4. Kc6 Kd4 (4... Ke2 5.
Bg2) 5. Kd6) 3. Ke6 Kc3 (3... Kd4 4. Kd6) 4. Kd7 Kb4 5. Kc6 Ka5 6. Bc4 Kb4 7.
Be2 Ka5 8. Bb5 Kb4 9. Kb6 $1 Kc3 10. Kc5 Kb3 11. Bc6 Kc3 12. Bd5 Kd3 13. Bf3
Kc3 14. Be2 Kb3 15. Bb5 Kc3 16. Bc4 Kb2 17. Kb4 Kc2 18. Bb5 Kb2 19. Ba4 Ka2 20.
Bd1 Kb2 21. Bb3 Ka1 22. Kc3 Kb1 23. Bd5 Ka1 24. Bc4 Kb1 25. Nd2+ Kc1 26. Bf1
Kd1 27. Nf3 Kc1 28. Nd4 Kb1 29. Nb5 Ka1 30. Na3 Ka2 31. Nc4 Kb1 32. Kd2 Ka1 33.
Kc1 Ka2 34. Kc2 Ka1 35. Kb3 Kb1 36. Nb2 Kc1 37. Kc3 Kb1 38. Nd3 Ka1 39. Kb4 $1
Ka2 40. Ka4 Ka1 41. Ka3 Kb1 42. Kb3 Ka1 43. Nc1 Kb1 44. Na2 Ka1 45. Ka3 Kb1 46.
Bd3+ Ka1 47. Nc1 f1=Q 48. Nb3# 1-0

But 3) remains unsolved (of course this is much more difficult to solve).

[peter]

But 3) remains unsolved (of course this is much more difficult to solve).

Took SlowChess being very quick as for solving that backwards and keeping DTM in output:

89003: Behting=C - (+0341.02g5c1) 1-0, Rigasche Rundschau 1905
8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

Analysis by SlowChess Blitz 2.9 avx2:

1.Kf6 Kc2 2.Ke7 Kd3 3.Ke6 Kc3 4.Kd7 Kb4 5.Kc6 Ka4 6.Lc4 Kb4 7.Le2 Ka4 8.Kb6 Kb4 9.Lb5 Ka3 10.Kc5 Kb3 11.Lc6 Kc2 12.Ld5 Kd3 13.Lf3 Kc3 14.Le2 Kb3 15.Lb5 Kc3 16.Lc4 Kb2 17.Kb4 Kc2 18.Lb5 Kb2 19.La4 Ka2 20.Ld1 Kb1 21.Kb3 Kc1 22.Lf3 Kb1 23.Ld5 Ka1 24.Ka3 Kb1 25.Le4+ Kc1 26.Kb3 Kd1 27.Ld3 Ke1 28.Kc3 Kd1 29.Se3+ Ke1 30.Sg2+ Kd1 31.Lf1 Kc1 32.Se3 Kb1 33.Sc4 Ka2 34.Kc2 Ka1 35.Kb3 Kb1 36.Sb2 Kc1 37.Kc3 Kb1 38.Sd3 Ka1 39.Kb4 Ka2 40.Ka4 Ka1 41.Ka3 Kb1 42.Kb3 Ka1 43.Sc1 Kb1 44.Sa2 Ka1 45.Ka3 Kb1 46.Ld3+ Ka1 47.Sc1 f1D 48.Sb3#
Tiefe: 86/105 00:01:39 3159MN, tb=6742449
+- (#48)

And MultiPV=2 :

8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

Analysis by SlowChess Blitz 2.9 avx2:

1. +- (#48): 1.Kf6! Kc2 2.Ke7 Kd3 3.Ke6 Kc3 4.Kd7 Kb4 5.Kc6 Ka4 6.Lc4 Kb4 7.Le2 Ka4 8.Kb6 Kb4 9.Lb5 Ka3 10.Kc5 Kb3 11.Lc6 Kc2 12.Ld5 Kd3 13.Lf3 Kc3 14.Le2 Kb3 15.Lb5 Kc3 16.Lc4 Kb2 17.Kb4 Kc2 18.Lb5 Kb2 19.La4 Ka2 20.Ld1 Kb1 21.Kb3 Kc1 22.Lf3 Kb1 23.Ld5 Ka1 24.Ka3 Kb1 25.Le4+ Kc1 26.Kb3 Kd1 27.Ld3 Ke1 28.Kc3 Kd1 29.Se3+ Ke1 30.Sg2+ Kd1 31.Lf1 Kc1 32.Se3 Kb1 33.Sc4 Ka2 34.Kc2 Ka1 35.Kb3 Kb1 36.Sb2 Kc1 37.Kc3 Kb1 38.Sd3 Ka1 39.Kb4 Ka2 40.Ka4 Ka1 41.Ka3 Kb1 42.Kb3 Ka1 43.Sc1 Kb1 44.Sa2 Ka1 45.Ka3 Kb1 46.Ld3+ Ka1 47.Sc1 f1D 48.Sb3#
2. = (0.02): 1.Kf4!? Kb2 2.Kg3 Kc1 3.Kg2 Kc2 4.Kxh1 Kc3 5.Lf3 Kb3 6.Lg2 Kc4 7.Le4 Kd4 8.Lc2 Kc3 9.Lf5 Kd4 10.Ld7 Kc3 11.Lh3 Kd3 12.Lg4 Kc3 13.Lh3

Of course only depth 42 in MultPV doesn't say so much as for the second one line, but giving in 1.Kf4?; this one move at least doesn't get any winning eval in depth 55 single primary neither, still with full hash (8G) out of backward of the main line.

1.Kf4?:

[d]8/8/8/3B4/5K2/8/5p1p/2k2Nbr b - - 0 1

Analysis by SlowChess Blitz 2.9 avx2:

1...Kb2 2.Ke3 Kc3 3.Le4 Kb4 4.Ke2 Kc5 5.Kf3 Kb5 6.Kg2 Kc4 7.Kxh1 Kd4 8.Lb7 Kc3 9.Lg2 Kd4 10.Lh3 Kd3 11.Lg4 Kd4 12.Ld1 Kd3 13.La4 Kd4 14.Le8 Ke5 15.Lh5 Kd4 16.Lf7 Kd3 17.Le6 Ke2 18.Lc4+ Kf3 19.Ld3 Kf4 20.Lc2 Ke5 21.Lg6 Kd4 22.Lb1 Kc3 23.La2 Kd4 24.Lg8 Kc3 25.Le6 Kd3 26.Ld7 Kd4 27.Lc8 Kc3 28.La6 Kd4 29.Lc8
Tiefe: 55/101 00:03:28 9755MN, tb=2943650
= (0.02)

Tried some times next best move- command from starting position with still DTM in output for best move, no other one first move getting a winning eval till depth 50, regards

[fkarger]

Thank you Peter!

Possibly Kf6 is the only move winning the decisive tempo.
But intuitively I would assume that there are other ways of getting it.

I will try to dig deeper.
Maybe SlowChess can help.

[Ajedrecista]

Hello:

What a problem! Firstly the knight tied on f1 square, then the bishop, lastly managing a K+B+N mating net somehow.

Regarding Chest 5.2 under Arena 2.0.1 GUI, I try a normal search and stop it; there are some output parameters ('Stellungs-Analyse'):

Code: Select all

FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

ChestUCI:
FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - -   (3+5)
Stellungs-Analyse:  C0/R0/K5/P1/X4   W:3/25
Suche nach Matt in 126 ...  (Hash=64MB)
Berechnung abgebrochen !

Then I go to 'Configure ChestUCI' (Ctrl+1) to change the search parameters:

Code: Select all

[...]
SearchMode = Special
ChecksOnly  = 0  // C in Stellungs-Analyse
ThreatDepth = 0  // R in Stellungs-Analyse
[...]
KingSquares = 5  // K in Stellungs-Analyse
PieceLimit  = 1  // P in Stellungs-Analyse
MaxMoves    = 4  // X in Stellungs-Analyse
[...]

There is no warrantee that this works, but it works sometimes. There is other option that is setting the KPX parameters as before and try SearchMode = Automatic or SearchMode = AutoTurbo, and Chest will iterate on some CR parameters while keeping KPX fixed.

I was not lucky this time with any of those search modes:

Code: Select all

FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

ChestUCI:
FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - -   (3+5)
Stellungs-Analyse:  C0/R0/K5/P1/X4   W:3/25
Suche nach Spezial-Matt [C0/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Suche abgeschlossen ...  (Zeit=0.00s)
Kein Matt in 126 gefunden !  (00:00)

Code: Select all

FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

ChestUCI:
FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - -   (3+5)
Stellungs-Analyse:  C0/R0/K5/P1/X4   W:3/25
Automatik-Suche nach Spezial-Matt [C1/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C2/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C4/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C8/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C16/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C0/R1/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C0/R2/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C0/R-2/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C0/R3/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C0/R-3/K5/P1/X4] in 126 ...  (Hash=64MB)
Automatik-Suche nach Spezial-Matt [C0/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Kein Matt in 126 gefunden !  (00:00)

Code: Select all

FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

ChestUCI:
FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - -   (3+5)
Stellungs-Analyse:  C0/R0/K5/P1/X4   W:3/25
AutoTurbo-Suche nach Spezial-Matt [C1/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
AutoTurbo-Suche nach Spezial-Matt [C0/R1/K5/P1/X4] in 126 ...  (Hash=64MB)
AutoTurbo-Suche nach Spezial-Matt [C0/R2/K5/P1/X4] in 126 ...  (Hash=64MB)
AutoTurbo-Suche nach Spezial-Matt [C0/R-2/K5/P1/X4] in 126 ...  (Hash=64MB)
AutoTurbo-Suche nach Spezial-Matt [C0/R3/K5/P1/X4] in 126 ...  (Hash=64MB)
AutoTurbo-Suche nach Spezial-Matt [C0/R-3/K5/P1/X4] in 126 ...  (Hash=64MB)
AutoTurbo-Suche nach Spezial-Matt [C0/R0/K5/P1/X4] in 126 ...  (Hash=64MB)
Kein Matt in 126 gefunden !  (00:00)

--------------------------------------------------

This problem is No. 869 in the 1968 edition of the book 1234 modern end-game studies compiled by M.A. Sutherland and H.M. Lommer. However, the given source disagrees with Peter's, this one saying J. Behting (not C. Behting) and year 1908 (not 1905), although they agree on 'Rigasche Rundschau' Latvian newspaper. The given solution is up to 46.- Bd3+, Ka1; 47.- Nc1.

More about this newspaper can be found here (filters applied to 1905 and 1908):

https://digitalabiblioteka.lv/?group=Ri ... in_page=50
https://digitalabiblioteka.lv/?group=Ri ... in_page=50

I did not find the problem searching 'Behting' fastly in that site. Maybe other year and/or other newspaper?

Regards from Spain.

Ajedrecista.

[Spliffjiffer]

with the given parameters, Chest finds no other mate within 126 moves !...so it seems pretty sure to me that 1.Kf6 !! is the only winning move !?
1.Kf5 and 1.Be4 seem to be 2nd best acc to Chest because black needs to find only moves (1.Kf5 Kc2!! and 1.Be4 Kb2!!)
analysis by Chest after 1.Kf6!! :

Code: Select all

FEN: 8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - 0 1

ChestUCI:
FEN: 8/8/5K2/3B4/8/8/5p1p/2k2Nbr b - - (3+5)
Stellungs-Analyse: S:1/4
Suche nach Spezial-Matt [C14/R0/K0/P1/X6] in -126 ... (Hash=2044MB)
Suche abgeschlossen ... (Zeit=16.90s)
Matt in -47 gefunden ! (8 Lösungen in 00:16)
 42/47	00:16	 30.315k	1.794k	-M42	1. ... Kc1-d1 2.Kf6-e5 Kd1-e2 3.Ld5-g2 Ke2-d3 4.Ke5-d5 Kd3-c3 5.Kd5-c5 Kc3-b3 6.Lg2-c6 Kb3-c3 7.Lc6-d5 Kc3-d3 8.Ld5-f3 Kd3-c3 9.Lf3-e2 Kc3-b3 10.Le2-b5 Kb3-c3 11.Lb5-c4 Kc3-b2 12.Kc5-b4 Kb2-c2 13.Lc4-e2 Kc2-b2 14.Le2-d1 Kb2-a2 15.Ld1-c2 Ka2-b2 16.Lc2-b3 Kb2-a1 17.Kb4-c3 Ka1-b1 18.Lb3-d5 Kb1-a1 19.Ld5-c4 Ka1-b1 20.Sf1-d2+ Kb1-c1 21.Lc4-f1 Kc1-d1 22.Sd2-f3 Kd1-c1 23.Sf3-d4 Kc1-b1 24.Sd4-b5 Kb1-c1 25.Sb5-a3 Kc1-d1 26.Sa3-c2 Kd1-c1 27.Sc2-e3 Kc1-b1 28.Se3-c4 Kb1-a2 29.Kc3-c2 Ka2-a1 30.Kc2-b3 Ka1-b1 31.Sc4-b2 Kb1-c1 32.Kb3-c3 Kc1-b1 33.Sb2-d3 Kb1-a1 34.Kc3-c4 Ka1-a2 35.Kc4-b4 Ka2-a1 36.Kb4-a3 Ka1-b1 37.Ka3-b3 Kb1-a1 38.Sd3-b4 Ka1-b1 39.Sb4-a2 Kb1-a1 40.Kb3-a3 Ka1-b1 41.Lf1-d3+ Kb1-a1 42.Sa2-c1 f2-f1D 43.Sc1-b3+
 42/47	00:16	 30.315k	1.794k	-M42	1. ... Kc1-d1 2.Kf6-e6 Kd1-e2 3.Ld5-g2 Ke2-d3 4.Ke6-d5 Kd3-c3 5.Kd5-c5 Kc3-b3 6.Lg2-c6 Kb3-c3 7.Lc6-d5 Kc3-d3 8.Ld5-f3 Kd3-c3 9.Lf3-e2 Kc3-b3 10.Le2-b5 Kb3-c3 11.Lb5-c4 Kc3-b2 12.Kc5-b4 Kb2-c2 13.Lc4-e2 Kc2-b2 14.Le2-d1 Kb2-a2 15.Ld1-c2 Ka2-b2 16.Lc2-b3 Kb2-a1 17.Kb4-c3 Ka1-b1 18.Lb3-d5 Kb1-a1 19.Ld5-c4 Ka1-b1 20.Sf1-d2+ Kb1-c1 21.Lc4-f1 Kc1-d1 22.Sd2-f3 Kd1-c1 23.Sf3-d4 Kc1-b1 24.Sd4-b5 Kb1-c1 25.Sb5-a3 Kc1-d1 26.Sa3-c2 Kd1-c1 27.Sc2-e3 Kc1-b1 28.Se3-c4 Kb1-a2 29.Kc3-c2 Ka2-a1 30.Kc2-b3 Ka1-b1 31.Sc4-b2 Kb1-c1 32.Kb3-c3 Kc1-b1 33.Sb2-d3 Kb1-a1 34.Kc3-c4 Ka1-a2 35.Kc4-b4 Ka2-a1 36.Kb4-a3 Ka1-b1 37.Ka3-b3 Kb1-a1 38.Sd3-b4 Ka1-b1 39.Sb4-a2 Kb1-a1 40.Kb3-a3 Ka1-b1 41.Lf1-d3+ Kb1-a1 42.Sa2-c1 f2-f1D 43.Sc1-b3+
 46/47	00:16	 30.315k	1.794k	-M46	1. ... Kc1-b2 2.Kf6-e7 Kb2-c3 3.Ke7-d7 Kc3-b4 4.Kd7-c6 Kb4-a4 5.Ld5-c4 Ka4-b4 6.Lc4-e2 Kb4-a4 7.Kc6-b6 Ka4-b4 8.Le2-b5 Kb4-a3 9.Kb6-c5 Ka3-b3 10.Lb5-c6 Kb3-c3 11.Lc6-d5 Kc3-d3 12.Ld5-f3 Kd3-c3 13.Lf3-e2 Kc3-b3 14.Le2-b5 Kb3-c3 15.Lb5-c4 Kc3-b2 16.Kc5-b4 Kb2-c2 17.Lc4-e2 Kc2-b2 18.Le2-d1 Kb2-a2 19.Ld1-c2 Ka2-b2 20.Lc2-b3 Kb2-a1 21.Kb4-c3 Ka1-b1 22.Lb3-d5 Kb1-a1 23.Ld5-c4 Ka1-b1 24.Sf1-d2+ Kb1-c1 25.Lc4-f1 Kc1-d1 26.Sd2-f3 Kd1-c1 27.Sf3-d4 Kc1-b1 28.Sd4-b5 Kb1-c1 29.Sb5-a3 Kc1-d1 30.Sa3-c2 Kd1-c1 31.Sc2-e3 Kc1-b1 32.Se3-c4 Kb1-a2 33.Kc3-c2 Ka2-a1 34.Kc2-b3 Ka1-b1 35.Sc4-b2 Kb1-c1 36.Kb3-c3 Kc1-b1 37.Sb2-d3 Kb1-a1 38.Kc3-c4 Ka1-a2 39.Kc4-b4 Ka2-a1 40.Kb4-a3 Ka1-b1 41.Ka3-b3 Kb1-a1 42.Sd3-b4 Ka1-b1 43.Sb4-a2 Kb1-a1 44.Kb3-a3 Ka1-b1 45.Lf1-d3+ Kb1-a1 46.Sa2-c1 f2-f1D 47.Sc1-b3+
 46/47	00:16	 30.315k	1.794k	-M46	1. ... Kc1-b2 2.Kf6-e6 Kb2-c3 3.Ke6-d7 Kc3-b4 4.Kd7-c6 Kb4-a4 5.Ld5-c4 Ka4-b4 6.Lc4-e2 Kb4-a4 7.Kc6-b6 Ka4-b4 8.Le2-b5 Kb4-a3 9.Kb6-c5 Ka3-b3 10.Lb5-c6 Kb3-c3 11.Lc6-d5 Kc3-d3 12.Ld5-f3 Kd3-c3 13.Lf3-e2 Kc3-b3 14.Le2-b5 Kb3-c3 15.Lb5-c4 Kc3-b2 16.Kc5-b4 Kb2-c2 17.Lc4-e2 Kc2-b2 18.Le2-d1 Kb2-a2 19.Ld1-c2 Ka2-b2 20.Lc2-b3 Kb2-a1 21.Kb4-c3 Ka1-b1 22.Lb3-d5 Kb1-a1 23.Ld5-c4 Ka1-b1 24.Sf1-d2+ Kb1-c1 25.Lc4-f1 Kc1-d1 26.Sd2-f3 Kd1-c1 27.Sf3-d4 Kc1-b1 28.Sd4-b5 Kb1-c1 29.Sb5-a3 Kc1-d1 30.Sa3-c2 Kd1-c1 31.Sc2-e3 Kc1-b1 32.Se3-c4 Kb1-a2 33.Kc3-c2 Ka2-a1 34.Kc2-b3 Ka1-b1 35.Sc4-b2 Kb1-c1 36.Kb3-c3 Kc1-b1 37.Sb2-d3 Kb1-a1 38.Kc3-c4 Ka1-a2 39.Kc4-b4 Ka2-a1 40.Kb4-a3 Ka1-b1 41.Ka3-b3 Kb1-a1 42.Sd3-b4 Ka1-b1 43.Sb4-a2 Kb1-a1 44.Kb3-a3 Ka1-b1 45.Lf1-d3+ Kb1-a1 46.Sa2-c1 f2-f1D 47.Sc1-b3+
 46/47	00:16	 30.315k	1.794k	-M46	1. ... Kc1-b1 2.Kf6-e7 Kb1-b2 3.Ke7-d7 Kb2-a3 4.Kd7-c7 Ka3-a4 5.Kc7-b6 Ka4-b4 6.Ld5-e6 Kb4-a4 7.Le6-d7+ Ka4-b4 8.Ld7-b5 Kb4-a3 9.Kb6-c5 Ka3-b3 10.Lb5-c6 Kb3-c3 11.Lc6-d5 Kc3-d3 12.Ld5-f3 Kd3-c3 13.Lf3-e2 Kc3-b3 14.Le2-b5 Kb3-c3 15.Lb5-c4 Kc3-b2 16.Kc5-b4 Kb2-c2 17.Lc4-e2 Kc2-b2 18.Le2-d1 Kb2-a2 19.Ld1-c2 Ka2-b2 20.Lc2-b3 Kb2-a1 21.Kb4-c3 Ka1-b1 22.Lb3-d5 Kb1-a1 23.Ld5-c4 Ka1-b1 24.Sf1-d2+ Kb1-c1 25.Lc4-f1 Kc1-d1 26.Sd2-f3 Kd1-c1 27.Sf3-d4 Kc1-b1 28.Sd4-b5 Kb1-c1 29.Sb5-a3 Kc1-d1 30.Sa3-c2 Kd1-c1 31.Sc2-e3 Kc1-b1 32.Se3-c4 Kb1-a2 33.Kc3-c2 Ka2-a1 34.Kc2-b3 Ka1-b1 35.Sc4-b2 Kb1-c1 36.Kb3-c3 Kc1-b1 37.Sb2-d3 Kb1-a1 38.Kc3-c4 Ka1-a2 39.Kc4-b4 Ka2-a1 40.Kb4-a3 Ka1-b1 41.Ka3-b3 Kb1-a1 42.Sd3-b4 Ka1-b1 43.Sb4-a2 Kb1-a1 44.Kb3-a3 Ka1-b1 45.Lf1-d3+ Kb1-a1 46.Sa2-c1 f2-f1D 47.Sc1-b3+
 46/47	00:16	 30.315k	1.794k	-M46	1. ... Kc1-b1 2.Kf6-e5 Kb1-b2 3.Ke5-d4 Kb2-a3 4.Kd4-c4 Ka3-a4 5.Kc4-c5 Ka4-a5 6.Ld5-c4 Ka5-a4 7.Kc5-b6 Ka4-b4 8.Lc4-b5 Kb4-a3 9.Kb6-c5 Ka3-b3 10.Lb5-c6 Kb3-c3 11.Lc6-d5 Kc3-d3 12.Ld5-f3 Kd3-c3 13.Lf3-e2 Kc3-b3 14.Le2-b5 Kb3-c3 15.Lb5-c4 Kc3-b2 16.Kc5-b4 Kb2-c2 17.Lc4-e2 Kc2-b2 18.Le2-d1 Kb2-a2 19.Ld1-c2 Ka2-b2 20.Lc2-b3 Kb2-a1 21.Kb4-c3 Ka1-b1 22.Lb3-d5 Kb1-a1 23.Ld5-c4 Ka1-b1 24.Sf1-d2+ Kb1-c1 25.Lc4-f1 Kc1-d1 26.Sd2-f3 Kd1-c1 27.Sf3-d4 Kc1-b1 28.Sd4-b5 Kb1-c1 29.Sb5-a3 Kc1-d1 30.Sa3-c2 Kd1-c1 31.Sc2-e3 Kc1-b1 32.Se3-c4 Kb1-a2 33.Kc3-c2 Ka2-a1 34.Kc2-b3 Ka1-b1 35.Sc4-b2 Kb1-c1 36.Kb3-c3 Kc1-b1 37.Sb2-d3 Kb1-a1 38.Kc3-c4 Ka1-a2 39.Kc4-b4 Ka2-a1 40.Kb4-a3 Ka1-b1 41.Ka3-b3 Kb1-a1 42.Sd3-b4 Ka1-b1 43.Sb4-a2 Kb1-a1 44.Kb3-a3 Ka1-b1 45.Lf1-d3+ Kb1-a1 46.Sa2-c1 f2-f1D 47.Sc1-b3+
 46/47	00:16	 30.315k	1.794k	-M46	1. ... Kc1-b1 2.Kf6-e6 Kb1-b2 3.Ke6-d6 Kb2-a3 4.Kd6-c6 Ka3-a4 5.Ld5-c4 Ka4-b4 6.Lc4-e2 Kb4-a4 7.Kc6-b6 Ka4-b4 8.Le2-b5 Kb4-a3 9.Kb6-c5 Ka3-b3 10.Lb5-c6 Kb3-c3 11.Lc6-d5 Kc3-d3 12.Ld5-f3 Kd3-c3 13.Lf3-e2 Kc3-b3 14.Le2-b5 Kb3-c3 15.Lb5-c4 Kc3-b2 16.Kc5-b4 Kb2-c2 17.Lc4-e2 Kc2-b2 18.Le2-d1 Kb2-a2 19.Ld1-c2 Ka2-b2 20.Lc2-b3 Kb2-a1 21.Kb4-c3 Ka1-b1 22.Lb3-d5 Kb1-a1 23.Ld5-c4 Ka1-b1 24.Sf1-d2+ Kb1-c1 25.Lc4-f1 Kc1-d1 26.Sd2-f3 Kd1-c1 27.Sf3-d4 Kc1-b1 28.Sd4-b5 Kb1-c1 29.Sb5-a3 Kc1-d1 30.Sa3-c2 Kd1-c1 31.Sc2-e3 Kc1-b1 32.Se3-c4 Kb1-a2 33.Kc3-c2 Ka2-a1 34.Kc2-b3 Ka1-b1 35.Sc4-b2 Kb1-c1 36.Kb3-c3 Kc1-b1 37.Sb2-d3 Kb1-a1 38.Kc3-c4 Ka1-a2 39.Kc4-b4 Ka2-a1 40.Kb4-a3 Ka1-b1 41.Ka3-b3 Kb1-a1 42.Sd3-b4 Ka1-b1 43.Sb4-a2 Kb1-a1 44.Kb3-a3 Ka1-b1 45.Lf1-d3+ Kb1-a1 46.Sa2-c1 f2-f1D 47.Sc1-b3+
 47/47	00:16	 30.315k	1.794k	-M47	1. ... Kc1-c2 2.Kf6-e7 Kc2-d3 3.Ke7-e6 Kd3-c3 4.Ke6-d7 Kc3-b4 5.Kd7-c6 Kb4-a4 6.Ld5-c4 Ka4-b4 7.Lc4-e2 Kb4-a4 8.Kc6-b6 Ka4-b4 9.Le2-b5 Kb4-a3 10.Kb6-c5 Ka3-b3 11.Lb5-c6 Kb3-c3 12.Lc6-d5 Kc3-d3 13.Ld5-f3 Kd3-c3 14.Lf3-e2 Kc3-b3 15.Le2-b5 Kb3-c3 16.Lb5-c4 Kc3-b2 17.Kc5-b4 Kb2-c2 18.Lc4-e2 Kc2-b2 19.Le2-d1 Kb2-a2 20.Ld1-c2 Ka2-b2 21.Lc2-b3 Kb2-a1 22.Kb4-c3 Ka1-b1 23.Lb3-d5 Kb1-a1 24.Ld5-c4 Ka1-b1 25.Sf1-d2+ Kb1-c1 26.Lc4-f1 Kc1-d1 27.Sd2-f3 Kd1-c1 28.Sf3-d4 Kc1-b1 29.Sd4-b5 Kb1-c1 30.Sb5-a3 Kc1-d1 31.Sa3-c2 Kd1-c1 32.Sc2-e3 Kc1-b1 33.Se3-c4 Kb1-a2 34.Kc3-c2 Ka2-a1 35.Kc2-b3 Ka1-b1 36.Sc4-b2 Kb1-c1 37.Kb3-c3 Kc1-b1 38.Sb2-d3 Kb1-a1 39.Kc3-c4 Ka1-a2 40.Kc4-b4 Ka2-a1 41.Kb4-a3 Ka1-b1 42.Ka3-b3 Kb1-a1 43.Sd3-b4 Ka1-b1 44.Sb4-a2 Kb1-a1 45.Kb3-a3 Ka1-b1 46.Lf1-d3+ Kb1-a1 47.Sa2-c1 f2-f1D 48.Sc1-b3+

tough problem and somewhat ununderstandable for me currently

[Dann Corbit]

ChestUCI prunes, so there is no guarantee that the mate is minimal.
I am not sure if it is guaranteed as unique for that depth.
Chest319 and Chest324 do no pruning but cannot solve mates as deep as that.
However, it is a proven mate (and a proof tree can be requested), so it is not like some chess engines which will suddenly change their minds and go from mate in 37 at ply 50 to mate in 64 at ply 51.
So it is a case of "no worse than mate in <x>"

[fkarger]

Thank you all!

Indeed it is a super tough problem.
So far I could not refute that Kf6 is the only winning move (using Sting, Crystal and Chest).

Crystal 080420 found mate with Kf6 at depth 42.
I will try Crystal with MultiPV=2 later.

[Spliffjiffer]

my current interpretation of this masterpiece id summerize similar to this:
1.black king wants to get to the 8th rank and if he manages to do so its a simple draw!(he managed to escape possible checks by the knight because of the pure massive distance)...to do so he tries to bypass the white king eighther on the left or the right side accordingly, therefore we need a central strong bishop
2.white needs his strong bishop controling the most important squares, the central ones, most importantly c4 and e4 and ocasionaly f3 and g2 if white decides to attack the knight, d5 (the bishop) is defended by his king
3.by having this central bishop (ideally on d5) white needs very precise maneuvering with his king to get (better sayed: to keep)the opposition to the black king as soon as he tries to drive out the bishop...therefore black tries to escape to b8 instead but this isnt possible anylonger because he will loose contact to the meanwhile unprotected d5-bishop which means that the white king easily stops him reaching the 8th by still having the (indirect) opposition
4.the rest is simple cyclic zugzwang doing the same stuff again and again (black is lost since he lost the opposition (better said: the opposition he never had) and not having contact to the d5-bishop...oc this is far from trivial if we consider the 50-move-rule but that shouldnt count here imo)
5.the endsequence is pretty difficult and i cant really explain it...sometimes one needs math himself

aditionally: to get the opposition we need to get "behind" the bishop because otherwise blacks king runs to the 8th...why 1.Kf5?! (the 1st move id really consider beyond 1.Kf6) looses the opposition and 1.Kf6!! does not i cant really explain...maybe someone other member can !?...if im not completely wrong with all this id assume that 1.Kf6!! is the ONLY winning move no matter if we consider the 50-move-rule or not !?
note: im human and make mistakes, if so feel free to critizise me, have a nice time,
Peer

[Dann Corbit]

Here is my data for the position:
8/8/8/3B2K1/8/8/5p1p/2k2Nbr w - - acd 97; bm Kf6; ce 32672; c0 "Rigasche Rundschau; 1905; Behting=C; (+0341.02g5c1); 1-0"; c3 "Kf6"; c4 "1"; c5 "Behting=C; 1-0"; c7 "Rigasche Rundschau;1905;W:Behting=C;(+0341.02g5c1);1-0;1905"; c8 "pv Kf6 Kc2 Ke7 Kd3 Ke6 Kc3 Kd7 Kb4 Kc6 Ka5 Bc4 Kb4 Be2 Ka5 Bb5 Kb4 Kb6 Kc3 Kc5 Kb3 Bc6 Kc3 Bd5 Kd3 Bf3 Kc3 Be2 Kb3 Bb5 Kc3 Bc4 Kb2 Kb4 Kc2 Bb5 Kb2 Ba4 Ka2 Bd1 Kb2 Bb3 Ka1 Kc3 Kb1 Bd5 Ka1 Bc4 Kb1 Nd2+ Kc1 Bf1 Kd1 Nf3 Kc1 Nd4 Kb1 Nb5 Ka1 Na3 Ka2 Nc4 Kb1 Kd2 Ka1 Kc1 Ka2 Kc2 Ka1 Kb3 Kb1 Nb2 Kc1 Kc3 Kb1 Nd3 Ka1 Kb4 Ka2 Ka4 Ka1 Ka3 Kb1 Kb3 Ka1 Nc1 Kb1 Na2 Ka1 Ka3 Kb1 Bd3+ Ka1 Nc1 f1=Q Nb3# 1-0"; c9 "HHdbVI.1634626.001a.88402"; dm 48; pm Kf6; pv Kf6 Kc2 Ke7 Kd3 Ke6 Kc3 Kd7 Kb4 Kc6 Ka5 Bc4 Kb4 Be2 Ka4 Kb6 Kb4 Bb5 Kc3 Kc5 Kb3 Bd7 Kc3 Bg4 Kd3 Bf3 Kc3 Be2 Kb3 Bb5 Kc3 Bc4 Kb2 Kb4 Kc2 Bb5 Kb2 Ba6 Ka2 Bc4+ Kb2 Bb3 Kc1 Kc3 Kb1 Bd5 Ka1 Bc4 Kb1 Nd2+ Kc1 Bf1 Kd1 Nf3 Kc1 Nd4 Kb1 Nb5 Kc1 Na3 Kd1 Nc2 Kc1 Ne3 Kb1 Nc4 Ka2 Kc2 Ka1 Kb3 Kb1 Nb2 Ka1 Nd3 Kb1 Kc3 Ka1 Kc4 Ka2 Kb4 Ka1 Ka3 Kb1 Kb3 Ka1 Nc1 Kb1 Na2 Ka1 Ka3 Kb1 Bd3+ Ka1 Nc1 f1=Q Nb3+;

To work a problem like this, I find the source problem if I can. This one is in HHdbVI. So I produced EPD records for each of the pv positions. Then I ran those positions from the final checkmate back to the original position. This gave me a new PV and I repeated the process with that one.
Some of Eduard's old SF solvers are the best SF clones for problem solving.
The comment c9 "HHdbVI.1634626.001a.88402" means that this position is found in HHdbVI, at (my) Epd row 1634626 which is the first move: 001a of game: 88402 in the set.
c8 is the original pv that came with the problem. and my pv is listed as pv.
I got mate in 48, same as everybody else.