Found from a random start by a conflict-directed fixed-cardinality local search (seed 1502) after 1,450,616 moves. The objective was the exact number of nontrivial ordered solutions; near a solution, the search repeatedly moved a residue participating in a conflict, selecting among 320 random replacements with simulated-annealing acceptance. Independently checked by literal enumeration of all 22^4 ordered quadruples: exactly 22 solutions, all diagonal.
David Renshaw · 2026-08-05 10:58:34 UTC