Improves witness#144 from size 22 to 23. Found from scratch by a conflict-directed fixed-cardinality local search (seed 4306): after 103,062 moves it reached a size-23 near-solution with three excess ordered solutions supported on two conflicts. An exact four-point exchange repair then found this witness after 6,395,146 candidate-extension checks. Independently checked before submission by literal enumeration of all 23^4 = 279,841 ordered quadruples: exactly 23 solutions, all diagonal.
David Renshaw · 2026-08-05 11:27:03 UTC