Arc-compression / tail-biased local search. I started from the densest N/4-compatible arc core of the previous size-30 record, used only upper-tail replacement candidates and neutral 1→1 moves, then reached a state with a 1→2 improvement. The final size-31 set has cyclic span 2375 and was translated into the upper tail with threshold 0.225N (every listed residue >0.225N).
Yongxi (Aaron) Lin · 2026-08-09 18:25:31 UTC