Errors in ChestDB or errors in analysis?

[Dann Corbit]

These two positions are supposed to be forced mate for the side to move.
But it seems I have found a fortress for both of them.
So is the analysis wrong, or is the database wrong?

[d]2N5/p4P2/p4RqP/P2krb2/5RNK/2PPB1P1/3P1pP1/4nQ2 b - - acd 73; acs 449; bm Nf3+; c2 "#-46; Defence; 00:03;"; ce 0; id "ChestDB.6538"; pm Nf3+; pv Nf3+ gxf3 Qh5+ Kxh5 Bg6+ Kxg6 Rg5+ Kh7 Rg7+ Kh8 Rh7+ Kg8 Rh8+ Kg7 Rh7+ Kf8 Rh8+ Ke7 Re8+ Kd7 Rd8+ Kc7 Rd7+ Kb8 Rb7+ Ka8 Rb8+ Kxa7 Rb7+ Kxa6 Ra7+ Kb5 Rxa5+ Kb4 Rb5+ Ka3 Rb3+ Ka2 Rb2+ Ka1 Ra2+ Kb1 Rb2+ Kc1 Rb1+ Kc2 Rb2+ Kd1 Rb1+ Ke2 Re1+ Kxf2 Re2+ Kg1 Rg2+;

[d]kB5K/2P4B/P4rP1/4r3/2N1n3/1RP4N/3b4/6RQ b - - acd 60; acs 50; bm Rf8+; c2 "#-67; Defence; 00:03;"; ce 0; id "ChestDB.6337"; pm Rf8+; pv Rf8+ Kg7 Bh6+ Kxh6 Rh5+ Kxh5 Rf5+ Ng5 Rxg5+ Kh6 Rxg6+ Kh5 Rg5+ Kh4 Rg4+ Kh3 Rg3+ Kh2 Rh3+ Kg2 Rg3+ Kf1 Rf3+ Ke1 Re3+ Kd1 Rd3+ Kc1 Rd1+ Kb2 Rd2+ Ka3 Ra2+ Kb4 Ra4+ Kb5 Ra5+ Kc6 Rc5+ Kd7 Rd5+ Ke6 Re5+ Kf7 Rf5+ Kg7 Rg5+ Bg6 Rxg6+ Kh8 Rg8+ Kh7 Rg7+ Kh6 Rg6+ Kh;

[F.Huber]

These two positions are supposed to be forced mate for the side to move.
But it seems I have found a fortress for both of them.
So is the analysis wrong, or is the database wrong?

No, these 2 are defence positions (#-46, UCI option 'DefenderMoves' checked), so that means the other side mates, not the side to move.
In the first example #-46 means, that whatever move black is making, white can mate in maximal 46 moves (for the best defence of black, in this case 1... Nf3+) - for any other black move white has an even shorter mate (in 7, 6 or less moves for this example).

Here's the full anlysis output of Arena for this first position (#-46):

ChestUCI Ver.5.2:
FEN: 2N5/p4P2/p4RqP/P2krb2/5RNK/2PPB1P1/3P1pP1/4nQ2 b - - (15+8)
Position-Analysis: B:4/24
Problem found in Database: #-46; Defence; 00:03;
Search for Special-Mate [C0/R0/K0/P0/X0] in -46 ... (Hash=256MB)
Search completed ... (Time=4.20s)
Mate in -46 found ! (37 Solutions in 00:04)
1/46 00:04 1.526.799 363.783 -M1 1. ... Qxf7 2.Rd6+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qxf7 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qh7 2.Rd6+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qh7 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qg8 2.Rd6+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qg8 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qg7 2.Rd6+
1/46 00:04 1.526.799 363.783 -M1 1. ... Qg7 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Re8 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Re7 2.Nxe7+
1/46 00:04 1.526.799 363.783 -M1 1. ... Re7 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Bxc8 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Bd7 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Bxg4 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Be4 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Nxd3 2.c4+
1/46 00:04 1.526.799 363.783 -M1 1. ... Nc2 2.c4+
2/46 00:04 1.526.799 363.783 -M2 1. ... Re4 2.R4xf5+ Re5 3.c4+
2/46 00:04 1.526.799 363.783 -M2 1. ... Re4 2.Ne7+ Rxe7 3.c4+
2/46 00:04 1.526.799 363.783 -M2 1. ... Re4 2.c4+ Rxc4 3.dxc4+
2/46 00:04 1.526.799 363.783 -M2 1. ... Re4 2.dxe4+ Bxe4 3.c4+
2/46 00:04 1.526.799 363.783 -M2 1. ... Bxd3 2.Qxd3+ Qxd3 3.Rd6+
2/46 00:04 1.526.799 363.783 -M2 1. ... Bxd3 2.c4+ Bxc4 3.Qxc4+
2/46 00:04 1.526.799 363.783 -M2 1. ... Nxg2+ 2.Qxg2+ Re4 3.c4+
3/46 00:04 1.526.799 363.783 -M3 1. ... Rxe3 2.R4xf5+ Qxf5 3.Rd6+ Kc5 4.d4+
3/46 00:04 1.526.799 363.783 -M3 1. ... Rxe3 2.c4+ Kc5 3.f8Q+ Re7 4.Qxe7+
6/46 00:04 1.526.799 363.783 -M6 1. ... Be6 2.Nxe5 Nf3+ 3.gxf3 Qh5+ 4.Kxh5 Bxf7+ 5.Ng6 Bxg6+ 6.Kxg6 Ke5 7.R4f5+
6/46 00:04 1.526.799 363.783 -M6 1. ... Qh5+ 2.Kxh5 Bxg4+ 3.Kxg4 Re6 4.f8Q Nxd3 5.Qd8+ Kc6 6.Nxa7+ Kb7 7.Qc8+
6/46 00:04 1.526.799 363.783 -M6 1. ... Qxg4+ 2.Rxg4 Nf3+ 3.gxf3 Be6 4.f8Q Rh5+ 5.Kxh5 Bf7+ 6.Qxf7+ Ke5 7.f4+
6/46 00:04 1.526.799 363.783 -M6 1. ... Qxf6+ 2.Nxf6+ Kc6 3.Rc4+ Rc5 4.Rxc5+ Kb7 5.Nd6+ Kb8 6.f8Q+ Bc8 7.Qxc8+
6/46 00:04 1.526.799 363.783 -M6 1. ... Qxh6+ 2.Nxh6 Nf3+ 3.gxf3 Be6 4.f8Q Rh5+ 5.Kxh5 Bf7+ 6.Qxf7+ Ke5 7.Qe6+
6/46 00:04 1.526.799 363.783 -M6 1. ... Qxh6+ 2.Rxh6 Nf3+ 3.gxf3 Re6 4.f8Q Rxh6+ 5.Nxh6 Bxc8 6.Qc5+ Ke6 7.Qh3+
7/46 00:04 1.526.799 363.783 -M7 1. ... Re6 2.Rxg6 Nf3+ 3.Rxf3 Bxg6 4.f8Q Kc6 5.Nxa7+ Kd7 6.Qc8+ Ke7 7.Bc5+ Rd6 8.Nc6+
7/46 00:04 1.526.799 363.783 -M7 1. ... Re6 2.f8Q Nf3+ 3.gxf3 Qh5+ 4.Kxh5 Bg6+ 5.Rxg6 Kc6 6.Nxa7+ Kc7 7.Qc8+ Kd6 8.Qd8+
7/46 00:04 1.526.799 363.783 -M7 1. ... Re6 2.R4xf5+ Qxf5 3.Rxf5+ Kc6 4.f8Q Nf3+ 5.Rxf3 Rxh6+ 6.Nxh6 Kc7 7.Rf7+ Kc6 8.Qc5+
7/46 00:04 1.526.799 363.783 -M7 1. ... Qg5+ 2.Kxg5 Nf3+ 3.Rxf3 Bxg4+ 4.Kxg4 Re6 5.f8Q Re4+ 6.dxe4+ Kxe4 7.Qe8+ Kd5 8.Qe6+
46/46 00:04 1.526.799 363.783 -M46 1. ... Nf3+ 2.gxf3 Qh5+ 3.Kxh5 Bg6+ 4.Kxg6 Rg5+ 5.Kh7 Rg7+ 6.Kh8 Rh7+ 7.Kg8 Rh8+ 8.Kg7 Rh7+ 9.Kf8 Rh8+ 10.Ke7 Re8+ 11.Kd7 Rd8+ 12.Kc7 Rd7+ 13.Kb8 Rb7+ 14.Ka8 Rb8+ 15.Kxa7 Rb7+ 16.Kxa6 Ra7+ 17.Kb5 Rxa5+ 18.Kb4 Rb5+ 19.Ka3 Rb3+ 20.Ka2 Rb2+ 21.Ka1 Ra2+ 22.Kb1 Rb2+ 23.Kc1 Rb1+ 24.Kc2 Rb2+ 25.Kd1 Rb1+ 26.Ke2 Re1+ 27.Kxf2 Re2+ 28.Kg1 Rg2+ 29.Kh1 Rg1+ 30.Kh2 Rh1+ 31.Kg2 Rg1+ 32.Kh3 Rxg3+ 33.Kh4 Rh3+ 34.Kg5 Rh5+ 35.Kg6 Rg5+ 36.Kh7 Rg7+ 37.Kh8 Rh7+ 38.Kg8 Rh8+ 39.Kg7 Rh7+ 40.Kg6 Rg7+ 41.Kh5 Rg5+ 42.Kh4 Rh5+ 43.Kg3 Rh3+ 44.Kf2 Rxf3+ 45.Ke2 Rxe3+ 46.Nxe3+ Ke5 47.d4+
Best move: Nf3, Value: -Mate in 46, Depth: 46/46, Time: 00:04,332, 1.526.799 Nodes, 363.783 N/sec

But if you really think you have found a 'fortress', then I would be curious to see it ...

Franz

[Dann Corbit]

Both fortresses are shown in the pvs supplied

[Eelco de Groot]

This is probably another case of Issue 501 It's becoming as famous as the jeans we used to wear.
To misquote Dann from a CCC post I believe it was: The birds have been working on my Mustang.

Somebody call the Stockfish Polizei

[F.Huber]

Both fortresses are shown in the pvs supplied

Well, I don't understand!?
Your pv (for the 1st problem) is exactly the same as the output from my ChestUCI solution, but it shows only the first 28 moves. After this 28th black move there's a #19 for white:
29.Kh1 Rg1+ 30.Kh2 Rh1+ 31.Kg2 Rg1+ 32.Kh3 Rxg3+ 33.Kh4 Rh3+ 34.Kg5 Rh5+ 35.Kg6 Rg5+ 36.Kh7 Rg7+ 37.Kh8 Rh7+ 38.Kg8 Rh8+ 39.Kg7 Rh7+ 40.Kg6 Rg7+ 41.Kh5 Rg5+ 42.Kh4 Rh5+ 43.Kg3 Rh3+ 44.Kf2 Rxf3+ 45.Ke2 Rxe3+ 46.Nxe3+ Ke5 47.d4+

So after 1... Nf3+ it's in fact a #46 for white - and that's exactly what the ChestUCI database states.
1... Nf3+ is the best defence for black with a following #46 for white, every other black moves leads to a shorter mate for white.

So what do I (or you) not understand correctly here?
Which 'fortress' have you found in this position???

Franz

[peter]