Helpmate tablebases Every solution to every position, precomputed.

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KNvknnn

6 pieces.

h#9.5
longest mate: h#8.5
deepest unique: 4
positions at that depth: h#8
deepest dual: h#7
deepest strict dual: 1,702,161,540
positions with a helpmate: 8,924,251
with a unique solution: 7,751,073,792
cells in the plane: 827,743,728 bytes
on disk

Deepest unique problems

h#8.5

7k/8/1n6/8/8/8/8/KNn1n3 w - - 0 1

Kb2 Kg7 Kc3 Kf6 Kd2 Ke5 Kd1 Kd4 Nd2 Kc3 Kxe1 Kb2 Kd1 Ka1 Kc2 Na2 Nb3#

pure model switchback self-block nocheck

h#8.5

7k/8/8/8/8/n7/1n6/K1n2N2 w - - 0 1

Kxb2 Kg7 Kxc1 Kf6 Kb2 Ke5 Kb3 Kd4 Ka4 Kc3 Ne3 Kb2 Kb4 Ka1 Kb3 Nb1 Nc2#

pure model ideal switchback closed-walk self-block nocheck

Note: the solution begins with a capture.

h#8.5

7k/8/8/n7/8/n7/Nn6/1K6 w - - 0 1

Kxb2 Kg7 Kc3 Kf6 Kb4 Ke5 Ka4 Kd4 Nb4 Kc3 Kxa5 Kb2 Ka4 Ka1 Kb3 Nb1 Nc2#

pure model ideal switchback self-block nocheck

Note: the side to move is in check in the diagram; the solution begins with a capture.

Deepest dual problems

Deepest dual with different first and last moves: h#7. The deepest dual overall is h#8, where the two solutions share a first or a last move.

Only one position exists at this depth.

h#7

8/8/5k2/8/3n4/n4N2/8/K1n5 b - - 0 1

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

Kf5 Kb2 Ke4 Kxa3 Kd3 Kb4 Kc2 Nxd4+ Kb1 Kc3 Ka1 Kc2 Na2 Nb3#
Ke6 Kb2 Kd5 Kxc1 Kc4 Kd2 Kb3 Nxd4+ Ka2 Kc3 Ka1 Kb3 Nb1 Nc2#

pure model ideal self-block