Plaskett's Puzzle Is No Longer Unsolvable by Engines (New?)

[mysammoore]

I'm not 100% sure I'm the first to discover this, but I also have not heard or read of anyone else noticing this:

As of 2025/2026, this famous puzzle: [d]8/3P3k/n2K3p/2p3n1/1b4N1/2p1p1P1/8/3B4 w - - 0 1 is no longer unsolvable from move 1 by engines. Conditions: Multi-PV off, so single root move, the engine has to come up with Nf6+ on its own, and, of course, show the winning line + evaluation. Under these conditions, with fresh TT, the engine never seeing this position before, both Reckless 0.10.0-devf260fbe52d2a and Lc0 0.32.1+git.dirty fd71a2d921b6 (using the largest network, BT4-it332), are able to find Nf6+ with a score of +4.00 or higher, showing the line 1. Nf6+ Kg7 2. Nh5+ Kg6 3. Bc2+ Kxh5, etc. On my machine it takes Reckless ~10 seconds to do this at 8 cores, and Lc0 about 20 (running on the GPU). Stockfish 19 is not able to see this using the same conditions for any amount of time until Nf6+ is put on the board.

Let me know if this is old news. Even so, it's always good to share, because I've been following this for 5 years and have never once seen an engine, let alone two, solve this from move 1.

[peter]

Latest thread about it was this one

viewtopic.php?p=997297#p997297

Took my own posting just because of the .pgn and the SlowChess- output, even if this one was copied after some Forward- Backward to get most reliable DTM, SlowChess also is one of the engines solving the puzzle on modern hardware the way you ask for.

Here

viewtopic.php?p=997290#p997290

e.g. I gave single thread- output of Stockfish and Reckless, started with empty hash, as well as one more of Lc0.

Guess the position is one of the most often discussed ones here, just give "Plaskett" or "Breukelen" a try with forum's search, regards

[mysammoore]

So I'm late by an entire month, then.

[peter]

Edited my posting still after you had already answered

[jhellis3]

Various versions of crystal have solved it for several years now (though some haven't)... Dev gets it in pretty short order.

[David Rabel]

Gaia 4.3.3 found it quite rapidly on my old 4770k

[Dann Corbit]

Stockfish found the key move in 2 seconds and a mate score by 2 minutes

Code: Select all

Analysis of C:\Users\Dcor\chess\epd\plasket.epd   
10/9/2026 3:45:38 PM Level: 15 Seconds
Analyzing engine: Stockfish-native

 1 Nf6+;                
    Searching move: Ng4-f6
    Best move (Stockfish-native): Ng4-f6
    Identical moves! Found in: 00:02
   Found 747 WDL and 741 DTZ tablebase files (up to 7-man).
   Available processors: 0-31:32-63
   Using 63 threads with NUMA node thread binding: 32/32:31/32
   NNUE evaluation using nn-134a887f4c8f.nnue (109MiB, (86896, 1024, 32, 32, 1))
   Network replica 1: Shared memory.
   Network replica 2: Shared memory.
     2/6	00:00	         32k	6,406k	+0.36	Nf6+  Kg7  d8Q
     3/8	00:00	         45k	7,563k	+0.04	Nf6+  Kg7  d8Q
     4/12	00:00	         58k	9,727k	-0.07	Nf6+  Kg7  d8Q
     5/10	00:00	         72k	12,024k	-0.32	Nf6+  Kg7  Nh5+  Kg6  d8Q
     6/10	00:00	         83k	13,779k	-0.55	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q
     7/14	00:00	        115k	16,430k	-1.38	Nf6+  Kg7  Nh5+  Kg6  Nf4+  Kf5  Bc2+  Kg4  Bd1+  Kxg3  d8Q
     8/20	00:00	        221k	16,985k	-1.41	d8Q  Nf7+  Ke7  Nxd8  Kxd8  Ba5+  Kd7  Bc7  Nxe3  Bxg3
     9/13	00:00	        221k	17,008k	-1.38	d8Q  Nf7+  Ke7  Nxd8  Kxd8  Ba5+  Kd7  Bc7  Nxe3  Bxg3  Nd5  Be5
    10/11	00:00	        221k	17,024k	-1.38	d8Q  Nf7+  Ke7  Nxd8  Kxd8  Ba5+  Kd7  Bc7  Nxe3  Bxg3
    11/12	00:00	        222k	17,044k	-1.38	d8Q  Nf7+  Ke7  Nxd8  Kxd8  Ba5+  Kd7  Bc7  Nxe3  Bxg3  Nd5
    12/46	00:00	      4,902k	38,300k	-3.40	Nxe3  Ba5  Be2  Nb8  Ke7  Nc6+  Kd6  Nd4  Bd3+  Kg7  Kxc5  Ngf3  Kc4  Ne6
    13/35	00:00	      6,134k	39,571k	-3.00	Nxe3  Ba5  Be2  Nb8  Bb5  Nf7+  Kxc5  Kg7  Ba4  Bc7
    14/19	00:00	      6,207k	39,789k	-3.23	Nxe3  Ba5  Be2  Nb8  Bb5  Kg7  Kxc5  Nf7  Ba4  Kf8  Kc4  Ke7  Kb5
    15/37	00:00	      8,046k	41,052k	-3.24	Nxe3  Ba5  Be2  Nb8  Ke7  Nc6+  Kd6  Nd4  Bd3+  Kg7  Kxc5  Ngf3  Kd5  Kf6  Ng4+  Ke7  Nxh6  Kxd7  Ng4  c2  Bxc2  Nxc2  Nf6+  Ke7  Nh5  Bd2
    16/41	00:00	      9,344k	41,531k	-3.38	Nxe3  Ba5  Be2  Nb8  Ke7  Nc6+  Kd6  Nd4  Bd3+  Kg7  Kxc5  Ngf3  Kd5  Kf6  Ng4+  Ke7  Nxh6  Kxd7  Ng4  c2  Nf2
    17/57	00:00	     24,226k	45,030k	-3.68	Nxe3  Ba5  Kc6  Nb8+  Kb5  Bd8  Bc2+  Kg8  Bf5  Be7  Kb6  Kf7  Kb7  Nxd7  Bxd7  Ne4  g4  Kf6  Ba4  Kg5  Kc6  Bf8  Kd5
    18/42	00:00	     42,658k	46,367k	-3.73	Nxe3  Ba5  Be2  Nb8  Ke7  Nc6+  Kd6  Nd4  Bd3+  Kg7  Kxc5  Ngf3  Nc4  Bd8  Ne3  Kf6  Nd5+  Ke5  Nxc3  Be7+  Kb6  Kd6  Kb7  Kxd7  Nd1  Kd6
    19/43	00:00	     44,364k	46,503k	-3.92	Nxe3  Ba5  Be2  Nb8  Ke7  Nc6+  Kd6  Nd4  Bd3+  Kg7  Kxc5  Ngf3  Nc4  Bd8  Ne3  Kf6  Nd5+  Ke5  Ne3
    20/54	00:01	     56,890k	46,554k	-3.99	Nxe3  Ba5  Be2  Nb8  Ke7  Nc6+  Kd6  Nd4  Bd3+  Kg7  Kxc5  Ngf3  Nc4  Bd8  Ne3  Kf6  Nd5+  Ke5  Nxc3  Be7+  Kb6  Kd6  Bg6
    21/58	00:02	    109,467k	46,384k	+4.76	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  c4+  Kd5  Kxg3  Qe5+  Kf3  Kxc4  Bc5  Qxc3  Kg2  Qe5  Bb6  Be4+  Kf2
    22/25	00:03	    145,568k	46,330k	+5.63	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Kh2  Qf4+  Kh1  Qxe3  Nf7+  Ke7  Ng5  Qe1+  Kg2
    23/43	00:05	    236,846k	46,340k	+6.39	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Bc5  Qg1+  Kf3  Bd1+  e2  Qf1+  Bf2  Qxe2+  Kg2  Qxc4  Nc5  Qg4+  Kf1  Bc2  Nge6  Qc4+  Kg2  Be4+  Kg1  Bf5  Nc7+  Kc6
    24/35	00:05	    237,383k	46,346k	+6.40	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nb8  Qe2  Kf4  Qh2+  Kg4  Bd1+  Kf5  Qe5+  Kg6  Bc2+  Kh5  Qxe3
    25/38	00:05	    238,515k	46,341k	+6.66	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nb8  Qe2  Nf7+  Kd5  Ng5  Qxe3+  Kg2  Qe2+  Kg3  Bd1  c2  Qxc2  Nd7  Qf5  Nb6+  Kc6  Nc4
    26/30	00:05	    240,670k	46,345k	+6.66	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nb8  Qe2  Kf4  Qh2+  Kg4  Bd1+  Kf5  Qe5+  Kg6  Bc2+  Kf7  Qf5+  Kg7  Qg6+  Kf8  Qxh6+  Ke8  Qxg5
    27/34	00:05	    243,811k	46,343k	+6.66	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Ba5  Qxa6  c4  Qxc4  Nh3  Qe2  Bb6  Be4  Nf2  Kd5  Kf4
    28/43	00:05	    249,037k	46,341k	+6.73	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Ba3  Qg1+  Kf4  Qh2+  Kg4  Qe2+  Kh4  Qxa6  Bc1  Qe2  h5  Qe1+  Kg4  Qxc1  e2  Kc6
    29/41	00:05	    250,848k	46,333k	+6.71	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nf3  Bd1  c4+  Kd5  Nc7+  Kc6  Nd4+  Kxc7  Ba3  Qxc4  c2  Bxc2  e2  Qd3+  Kh2  Qe4  Bc1
    30/40	00:05	    255,080k	46,328k	+6.79	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nf3  Bd1  c4+  Kd5  Nc7+  Kc6  Nd4+  Kxc7  Ba3  Qxc4  c2  Bxc2  e2  Qd3+  Kg2  Qe4+  Kg3  Qe3+  Kg4  Qxd4+  Kf3  Be4+  Kg3
    31/41	00:05	    263,516k	46,288k	+6.81	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Nc7+  Kxc4  Nce6  Qg1+  Kf3  Bd1+  e2  Qf1+  Kg3  Qe1+  Kh3  Qxe2  Bd6  Qd3+  Bg3  Qf1+  Kh2
    32/39	00:06	    281,157k	46,266k	+6.99	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Bf8  Qg1+  Kf3  Bd1+  e2  Qf1+  Kg3  Qe1+  Kg2  Qxe2+  Kg1  Kxc4  Bg7  Qg4+  Kf1  Qf4+  Ke1
    33/45	00:06	    297,197k	46,256k	+7.16	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Nf3  Bd1  Nc7+  Kc6  Nd4+  Kxc7  Be7  Qg1+  Kf4  Qg4+  Ke5  Qg7+  Bf6  Qxh6  Ne6+  Kd7  Nf4  Bc2  Nd5
    34/45	00:07	    331,475k	46,096k	+7.16	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Nf3  Bd1  Nc7+  Kc6  Nd4+  Kxc7  Be7  Qg1+  Kf4  Qg4+  Ke5  Qg7+  Bf6  Qxh6  Ne6+  Kd7  Nc5+  Kc6
    35/45	00:07	    362,002k	45,916k	+7.20	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nf3  Bd1  c4+  Kd5  Nc7+  Kc6  Nd4+  Kxc7  Be7  Qg1+  Kf4  Qg4+  Ke5  Qg7+  Bf6  Qxh6  Ne6+  Kc6  Nf4  Qf8  Ke4  Qxf6  e2  Bxe2  c2
    36/46	00:09	    417,287k	45,705k	+7.26	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nc7  Kxc7  Ne6+  Kd6  Nd4  Bd1  e2  Bxe2  c2  Qg1+  Kf4  Bd3  c4+  Kd5  Nf3  Qc1+  Bd2  Qxc2  c3  Qa4+  Kg3  Qd1  Ne1  Be4  Kf2  Qh5  c2
    37/38	00:09	    452,444k	45,582k	+7.17	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nc7  Kxc7  Ne6+  Kd6  Nd4  Bd1  e2  Bxe2  c2  Qg1+  Kf4  Bd3  c4+  Kd5  Nf3  Qc1+  Bd2  Qxc2  c3  Qa4+  Ke3  Qe4+  Kf2  Qe2+  Kg3  Be4
    38/41	00:11	    530,009k	45,647k	+7.20	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nc7  Kxc7  Ne6+  Kd6  Nd4  Bd1  e2  Bxe2  c2  Qg1+  Kf4  Bd3  c4+  Kd5  Nf3  Qc1+  Bd2  Qxc2  c3  Be4  Ne1
    39/41	00:13	    615,547k	45,677k	+7.57	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Nf3  Bd1  Nc7+  Kc6  Nd4+  Kxc7  Be7  Qg1+  Kf4  Qg4+  Ke5  Qg7+  Bf6  Qxh6  Ne6+  Kd7  Nf4  Bc2  e2  Qf8  Nd3  Qe8+  Kf4
    40/52	00:18	    860,244k	45,583k	+7.76	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Nf3  Bd1  Nc7+  Kc6  Nd4+  Kxc7  Be7  Qg1+  Kf4  Qg4+  Ke5  Qg7+  Bf6  Qxh6  Ke6  Qxe3+  Be5+  Kb6  Nf5  Qf3  Nd6  Qg4+  Ke7
    41/47	00:23	  1,076,094k	45,555k	+7.59	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nf3  Bd1  c4+  Kd5  Nc7+  Kc6  Nd4+  Kxc7  Be7  Qg1+  Kf4  Qg4+  Ke5  Qg7+  Bf6  Qxh6  e2  Bxe2  Nf5  Qh2+  Kd5  Qg2+  Ke5  Bxc4  Ne3  Qe2
    42/43	00:25	  1,145,253k	45,548k	+8.05	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nf3  Bd1  c4+  Kd5  Nc7+  Kc6  Nd4+  Kxc7  c2  Qg1+  Kf4  Qh2+  Ke4  Bxc2+  Nxc2  Qxc2+  Kd4  Qe2  Bd2  Kc6  c3  Kb5  Kd5  Qd3+  Ke5  Kc4  Kf4  Qd6+  Kf3  Qd5+  Kf2
    43/52	00:42	  1,944,597k	45,693k	+8.41	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  Nf3  Bd1  c4+  Kd5  Nc7+  Kc6  Ne5+  Kxc7  Be7  Qe1+  Kf4  Qxc3  Bf6  Qd4+  Kf5  Qxe3  Kg6  Bc2+  Kg7  Kd6  Nf7+  Kd5  Nd8  Qc5  Bg5
    44/49	00:55	  2,523,242k	45,801k	+9.04	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qf1  c4+  Kd5  Nf3  Bd1  Nc7+  Kc6  Ne5+  Kxc7  Be7  Qe1+  Kf4  Qxc3  Bc5  Qa5  Bf8  Qd5  c3  Qd4+  Kf5  Bc2+  Ke6  Qxe3  Bg7  Qb6+  Kd5  Qf2  Ke6  Bb3+  Ke7  Qh4+  Bf6  Qxh6
    45/54+	01:11	  3,290,808k	46,007k	+10.70	Nf6+
    45/61+	01:19	  3,643,060k	46,044k	+13.02	Nf6+
    45/61+	01:20	  3,698,578k	46,011k	+85.62	Nf6+
    45/61-	01:20	  3,699,063k	46,011k	+57.29	Nf6+  Kg7
    45/61-	01:20	  3,699,065k	46,011k	+57.29	Nf6+  Kg7
    45/61	02:04	  5,501,812k	44,203k	+199.51	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qe5+  Kf3  Qf5+  Kg3  Bd1  Nb8  Qg4+  Kh2  Qe2+  Kh1  Qxe3  Kg2  Kc7  Na6+  Kb7  Nc7  Kxc7  Ba5+  Kc6  Bb4  Kd5  c4  Qe2+  Kg3  Qg4+  Kf2  Qh4+  Kg1  Qxc4  Bf8  Qg4+  Kf2  Qf5+  Kg3  Qxf8  Nh3  Qg7+  Kf2  Qxh6  Ng1  Qf6+  Ke3  Qd4+
    46/50	02:43	  6,961,446k	42,589k	+199.55	Nf6+  Kg7  Nh5+  Kg6  Bc2+  Kxh5  d8Q  Kg4  Qf6  Kxg3  Qe5+  Kf2  Qf4+  Ke2  Qg4+  Ke1  Ke5  c4  Bd1  Kf2  Kd5  Bf8  Qe2+  Kg3  Qxe3+  Kg2  Qe2+  Kg1  Kxc4  Nc5  Qg4+  Kf2  Qf4+  Ke1  Qxf8  Nge4  Bc2  Nd7  Qxh6  Ne5+  Kd5  Ng4  Qc1+  Kf2  Kxe4  Nh2  Qe3+  Kg2  Qxc3  Nf1  Kf4  Nh2  Qg3+  Kh1  Be4+  Nf3  Bxf3+
   10/9/2026 3:51:50 PM, Time for this analysis: 00:03:00, Rated time: 00:02

1 of 1 matching moves
10/9/2026 3:51:51 PM, Total time: 12:06:12 AM
Rated time: 00:02 = 2 Seconds

[Dann Corbit]

CSTal-2.07-cst-absurd-AVX2 and CSTal-2.07-cst-extreme-AVX2 both found the key move very quickly

All of Eduard's engines can solve it, though a couple of them fail high but never return from the search.