What's the shortest mate?

[David Dahlem]

[d] 8/2ppppp1/rpR3k1/8/8/6p1/5pP1/7K b - - 0 1

This is supposed to be a mate in 16. Lots of engines find a mate in 18, but i haven't found one that finds mate in 16. This is what i have for the solution -

1...d6 2.Rxd6+ f6 3.Rxf6+ Kh7 4.Rh6+ Kg8 5.Rh8+ Kf7 6.Rf8+ Ke6 7.Rf6+ Kd7 8.Rd6+ Kc8 9.Rd8+ Kb7 10.Rb8+ Kc6 11.Rxb6+ Kd7 12.Rd6+ Ke8 13.Rd8+ Kf7 14.Rf8+ Kg6 15.Rf6+ Kh7 16.Rh6+ Rxh6#

Strangely, The ProDeo Mate engine finds a mate in 17, then switches to mate in 18.

FEN: 8/2ppppp1/rpR3k1/8/8/6p1/5pP1/7K b - - 0 1
ProDeo Mate:
14 00:07 5.144.765 651.236 -M17 d7d6 Rc6xd6+ f7f6 Rd6xf6+ Kg6h7 Rf6h6+ Kh7g8 Rh6h8+ Kg8f7 Rh8f8+ Kf7e6 Rf8f6+ Ke6d7 Rf6d6+ Kd7c8 Rd6d8+ Kc8b7 Rd8b8+ Kb7c6 Rb8xb6+ Kc6d7 Rb6d6+ Kd7e8 Rd6d8+
15 00:08 5.476.412 651.953 -M17 d7d6 Rc6xd6+ f7f6 Rd6xf6+ Kg6h7 Rf6h6+ Kh7g8 Rh6h8+ Kg8f7 Rh8f8+ Kf7xf8
14 00:08 4.887.579 565.038 -6.41 d7d6
16 00:09 7.297.625 737.133 -M17 d7d6 Rc6xd6+ f7f6 Rd6xf6+ Kg6h7 Rf6h6+ Kh7g8 Rh6h8+ Kg8f7 Rh8f8+ Kf7e6 Rf8f6+ Ke6d7 Rf6d6+ Kd7c8 Rd6d8+ Kc8b7 Rd8b8+ Kb7c6 Rb8xb6+ Kc6d7 Rb6d6+ Kd7e8 Rd6d8+
17 00:12 9.763.263 787.359 -M17 d7d6 Rc6xd6+ f7f6 Rd6xf6+ Kg6h7 Rf6h6+ Kh7g8 Rh6h8+ Kg8f7 Rh8f8+ Kf7e6 Rf8f6+ Ke6d5 Rf6d6+ Kd5e5 Rd6d1 b6b5 Rd1d5+ Ke5e6 Rd5e5+ Ke6d7 Re5xe7+ Kd7c8 Re7e8+
18 01:04 51.254.206 800.846 -M18 d7d6 Rc6xd6+ f7f6 Rd6xf6+ Kg6h7 Rf6h6+ Kh7g8 Rh6h8+ Kg8f7 Rh8f8+ Kf7e6 Rf8f6+ Ke6d7 Rf6d6+ Kd7c8 Rd6d1 b6b5 Rd1d8+ Kc8b7 Rd8b8+ Kb7c6 Rb8b6+ Kc6d7 Rb6d6+
19 01:18 66.853.820 857.100 -M18 d7d6 Rc6xd6+ f7f6 Rd6xf6+ Kg6h7 Rf6h6+ Kh7g8 Rh6h8+ Kg8f7 Rh8f8+ Kf7e6 Rf8f6+ Ke6d7 Rf6d6+ Kd7c8 Rd6d1 c7c5 Rd1d8+ Kc8b7 Rd8b8+ Kb7c6 Rb8xb6+ Kc6d5 Rb6d6+

I tried the Chest mate solver without success. Perhaps i didn't wait long enough. Anyone care to test this for shortest mate?

[noctiferus]

Very strange:
output from Chest 4.4.1:
WinCHEST Ver.3.19f+, 01-Feb-2006
Options = -M256 -Z38 -1 -eL -0 -5 -SUr
Input file: STDIN
Reading job:
% created by ChestUCI Ver.4.4
W: Kh1 Rc6 Pg2 (3)
B: Kg6 Ra6 Pb6 Pc7 Pd7 Pe7 Pf7 Pf2 Pg7 Pg3 (10)
FEN: 8/2ppppp1/rpR3k1/8/8/6p1/5pP1/7K b - -
analysing (first mate in 38 moves):
Solution (in 18 moves):
d7d6
Time (virt) = 167.859 sec (ca. 2.8 min)

PV= d7d6 c6d6 f7f6 d6f6 g6h7 f6h6 h7g8 h6h8 g8f7 h8f8 f7e6 f8f6 e6d7 f6d6 d7c8 d6d1 b6b5 d1d8 c8b7 d8b8 b7c6 b8b6 c6d7 b6d6 d7e8 d6d8 e8f7 d8f8 f7g6 f8f6 g6h7 f6f2 a6a1 f2f1 a1f1
d7d6 c6d6 f7f6 d6f6 g6h7 f6h6 h7g8 h6h8 g8f7 h8f8 f7e6 f8f6 e6d7 f6d6 d7c8 d6d1 b6b5 d1d8 c8b7 d8b8 b7c6 b8b6 c6d7 b6d6 d7e8 d6d8 e8f7 d8f8 f7g6 f8f6 g6h7 f6f2 a6a1 f2f1 a1f1
f6a6 f2f1q
f6b6 f2f1q
f6c6 f2f1q
f6d6 f2f1q
f6e6 f2f1q
f6f3 a6a1
f6f4 a6a1
f6f5 a6a1
f6f7 a6a1
f6f8 a6a1
f6g6 f2f1q
f6h6 a6h6
f8f2 a6a1 f2f1 a1f1
f8a8 f2f1q
f8b8 f2f1q
f8c8 f2f1q
f8d8 f2f1q
f8e8 f2f1q
f8f3 a6a1
f8f4 a6a1
f8f5 a6a1
f8f7 a6a1
f8g8 f2f1q
f8h8 f2f1q
d8a8 f2f1q
d8b8 f2f1q
d8c8 f2f1q
d8d1 a6h6
d8d2 f2f1q
d8d3 f2f1q
d8d4 f2f1q
d8d5 f2f1q
d8d6 f2f1q
d8d7 f2f1q
d8e8 f2f1q
d8g8 f2f1q
d8h8 f2f1q
d6a6 f2f1q
d6b6 f2f1q
d6c6 f2f1q
d6d1 a6h6
d6d2 f2f1q
d6d3 f2f1q
d6d4 f2f1q
d6d5 f2f1q
d6d7 f2f1q
d6e6 f2f1q
d6f6 a6a1
d6g6 f2f1q
d6h6 f2f1q
b6a6 f2f1q
b6b5 f2f1q
b6b7 f2f1q
b6b8 f2f1q
b6c6 f2f1q
b6e6 f2f1q
b6f6 a6a1
b6g6 f2f1q
b6h6 f2f1q
b8a8 f2f1q
b8b5 f2f1q
b8b7 f2f1q
b8c8 f2f1q
b8d8 f2f1q
b8e8 f2f1q
b8f8 a6a1
b8g8 f2f1q
b8h8 f2f1q
d8a8 f2f1q
d8c8 f2f1q
d8d1 a6h6
d8d2 f2f1q
d8d3 f2f1q
d8d4 f2f1q
d8d5 f2f1q
d8d6 f2f1q
d8d7 f2f1q
d8e8 f2f1q
d8f8 a6a1
d8g8 f2f1q
d8h8 f2f1q
d1a1 a6a1
d1b1 a6h6
d1c1 a6h6
d1d2 f2f1q
d1d3 f2f1q
d1d4 f2f1q
d1d5 f2f1q
d1d6 f2f1q
d1d7 f2f1q
d1e1 f2e1q
d1f1 a6h6
d1g1 a6h6
d6d8 c8b7 d8b8 b7c6 b8b6 c6d7 b6d6 d7e8 d6d8 e8f7 d8f8 f7g6 f8f6 g6h7 f6f2 a6a1 f2f1 a1f1
f6a6 f2f1q
f6b6 f2f1q
f6c6 f2f1q
f6d6 f2f1q
f6e6 f2f1q
f6f3 a6a1
f6f4 a6a1
f6f5 a6a1
f6f7 a6a1
f6f8 a6a1
f6g6 f2f1q
f6h6 a6h6
f8f2 a6a1 f2f1 a1f1
f8a8 f2f1q
f8b8 f2f1q
f8c8 f2f1q
f8d8 f2f1q
f8e8 f2f1q
f8f3 a6a1
f8f4 a6a1
f8f5 a6a1
f8f7 a6a1
f8g8 f2f1q
f8h8 f2f1q
d8a8 f2f1q
d8b8 f2f1q
d8c8 f2f1q
d8d1 a6h6
d8d2 f2f1q
d8d3 f2f1q
d8d4 f2f1q
d8d5 f2f1q
d8d6 f2f1q
d8d7 f2f1q
d8e8 f2f1q
d8g8 f2f1q
d8h8 f2f1q
d6a6 f2f1q
d6b6 f2f1q
d6c6 f2f1q
d6d1 a6h6
d6d2 f2f1q
d6d3 f2f1q
d6d4 f2f1q
d6d5 f2f1q
d6d7 f2f1q
d6e6 f2f1q
d6f6 a6a1
d6g6 f2f1q
d6h6 f2f1q
b6a6 f2f1q
b6b1 a6h6
b6b2 f2f1q
b6b3 f2f1q
b6b4 f2f1q
b6b5 f2f1q
b6b7 f2f1q
b6b8 f2f1q
b6c6 f2f1q
b6e6 f2f1q
b6f6 a6a1
b6g6 f2f1q
b6h6 f2f1q
b8a8 f2f1q
b8b7 f2f1q
b8c8 f2f1q
b8d8 f2f1q
b8e8 f2f1q
b8f8 a6a1
b8g8 f2f1q
b8h8 f2f1q
d8d1 b6b5 d1a1 a6a1
d1b1 a6h6
d1c1 a6h6
d1d2 f2f1q
d1d3 f2f1q
d1d4 f2f1q
d1d5 f2f1q
d1d6 f2f1q
d1d7 f2f1q
d1d8 f2f1q
d1e1 f2e1q
d1f1 a6h6
d1g1 a6h6
d8a8 f2f1q
d8c8 f2f1q
d8d2 f2f1q
d8d3 f2f1q
d8d4 f2f1q
d8d5 f2f1q
d8d6 f2f1q
d8d7 f2f1q
d8e8 f2f1q
d8f8 a6a1
d8g8 f2f1q
d8h8 f2f1q
d6b6 f2f1q
d6c6 f2f1q
d6d2 f2f1q
d6d3 f2f1q
d6d4 f2f1q
d6d5 f2f1q
d6d7 f2f1q
d6e6 f2f1q
d6f6 a6a1
d6g6 f2f1q
d6h6 f2f1q
f6f2 a6a1 f2f1 a1f1
f6b6 f2f1q
f6c6 f2f1q
f6e6 f2f1q
f6f3 a6a1
f6f4 a6a1
f6f5 a6a1
f6f7 a6a1
f6f8 a6a1
f6g6 f2f1q
f6h6 f2f1q
f8f2 a6a1 f2f1 a1f1
f8a8 f2f1q
f8b8 f2f1q
f8c8 f2f1q
f8d8 f2f1q
f8e8 f2f1q
f8f3 a6a1
f8f4 a6a1
f8f5 a6a1
f8f7 a6a1
f8g8 f2f1q
f8h8 f2f1q
h8a8 f2f1q
h8b8 f2f1q
h8c8 f2f1q
h8d8 f2f1q
h8e8 f2f1q
h8g8 f2f1q
h8h2 f2f1q
h8h3 f2f1q
h8h4 f2f1q
h8h5 f2f1q
h8h6 f2f1q
h8h7 f2f1q
h6b6 f2f1q
h6c6 f2f1q
h6d6 f2f1q
h6e6 f2f1q
h6f6 a6a1
h6g6 f2f1q
h6h2 f2f1q
h6h3 f2f1q
h6h4 f2f1q
h6h5 f2f1q
h6h7 f2f1q
f6f2 a6a1 f2f1 a1f1
f6b6 f2f1q
f6c6 f2f1q
f6d6 f2f1q
f6e6 f2f1q
f6f3 a6a1
f6f4 a6a1
f6f5 a6a1
f6f7 a6a1
f6f8 a6a1
f6g6 f2f1q
d6d1 a6a8 d1a1 a8a1
d1b1 a8h8
d1c1 a8h8
d1d2 f2f1q
d1d3 f2f1q
d1d4 f2f1q
d1d5 f2f1q
d1d6 f2f1q
d1d7 f2f1q
d1d8 f2f1q
d1e1 f2e1q
d1f1 a8h8
d1g1 a8h8
d6b6 f2f1q
d6c6 f2f1q
d6d2 f2f1q
d6d3 f2f1q
d6d4 f2f1q
d6d5 f2f1q
d6d7 f2f1q
d6d8 f2f1q
d6e6 f2f1q
c6c1 a6a8 c1a1 a8a1
c1b1 a8h8
c1c2 f2f1q
c1c3 f2f1q
c1c4 f2f1q
c1c5 f2f1q
c1c6 f2f1q
c1c7 f2f1q
c1d1 a8h8
c1e1 f2e1q
c1f1 a8h8
c1g1 a8h8
c6b6 f2f1q
c6c2 f2f1q
c6c3 f2f1q
c6c4 f2f1q
c6c5 f2f1q
c6c7 f2f1q

end of solution tree (no duals except at top)
Total Time (virt) = 167.859 sec (ca. 2.8 min)


are yo sure that the mates in 16 or 17 moves are correct (no way to delay mate?)

[David Dahlem]

No, i'm not sure my solution is correct, it's the solution from the composer of this position. Since i can't verify it with any engine, the solution may not be correct. That's why i posted it.

[noctiferus]

This would be the first time I see Chest going astray: AFAIK, he makes an extensive (non pruned) search. I'll try to check your solution ste by step.

[Jim Walker]

I believe it's a mate in 18. The problem with your mate is 16 Rh6+ is wrong. To delay mate white plays Rxf2.
Jim

[noctiferus]

Txs for saving my time ifor the analysis

[F.Huber]

I believe it's a mate in 18. The problem with your mate is 16 Rh6+ is wrong. To delay mate white plays Rxf2.
Jim

Yes, it's indeed a #18. But the wrong move in the original solution is already 9.Rd8+.

Here's the ChestUCI solution:
8/2ppppp1/rpR3k1/8/8/6p1/5pP1/7K b - - bm #18; 00:05 @ C0/R1/K1/P1/X14;

1...d6 2.Rxd6+ f6 3.Rxf6+ Kh7 4.Rh6+ Kg8 5.Rh8+ Kf7 6.Rf8+ Ke6 7.Rf6+ Kd7 8.Rd6+ Kc8 9.Rd1 b5 10.Rd8+ Kb7 11.Rb8+ Kc6 12.Rb6+ Kd7 13.Rd6+ Ke8 14.Rd8+ Kf7 15.Rf8+ Kg6 16.Rf6+ Kh7 17.Rxf2 Ra1+ 18.Rf1 Rxf1#

[Jim Walker]

Yes all engines I checked wanted to play Rd1 instead of Rd8.
Jim

[F.Huber]

% created by ChestUCI Ver.4.4

Any special reason to use such an ancient ChestUCI version?

The latest one is 5.1 from April 2008.

[noctiferus]

No, simply I didn't update it. txs