Helpmate tablebases Every solution to every position, precomputed.

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KPvkb

4 pieces.

h#8.5
longest mate: h#7.5
deepest unique: 13
positions at that depth: h#7.5
deepest dual: h#7.5
deepest strict dual: 9,426,908
positions with a helpmate: 97,387
with a unique solution: 5,548,032
cells in the plane: 5,159,141 bytes
on disk

Deepest unique problems

h#7.5

8/8/1K6/8/2b5/2P5/7k/8 w - - 0 1

Ka5 Bd5 c4 Kg3 cxd5 Kf4 d6 Ke5 d7 Kd6 Kb5 Kc7 Ka6 Kb8 d8=Q#

set-play pure model ideal mirror promotion nocheck umnov

h#7.5

6k1/8/8/8/8/3b4/3P4/1K6 w - - 0 1

Kc1 Be4 d3 Kf7 dxe4 Ke6 e5 Kd5 e6 Kc4 e7 Kb3 e8=Q Ka2 Qa4#

pure model ideal mirror promotion excelsior excelsior:white nocheck umnov

Note: the side to move is in check in the diagram.

h#7.5

8/K7/8/8/8/7b/3P4/7k w - - 0 1

d4 Kg2 d5 Kf3 d6 Ke4 d7 Kd5 d8=Q+ Kc6 Qd5+ Kc7 Ka6 Kb8 Qb7#

promotion excelsior excelsior:white closed-walk single-piece single-piece:black nocapture umnov

Deepest dual problems

Only one position exists at this depth.

h#7.5

6k1/8/8/8/8/3b4/1K1P4/8 w - - 0 1

Two solutions, with different first and last moves (2 starts, 2 ends).

Kc1 Be4 d3 Kf7 dxe4 Ke6 e5 Kd5 e6 Kc4 e7 Kb3 e8=Q Ka2 Qa4#
Kc3 Bc4 d3 Kf7 dxc4 Ke6 c5 Kd5 c6 Kc5 c7 Kb5 c8=Q Ka4 Qa6#

pure model ideal mirror promotion excelsior excelsior:white nocheck umnov