Claude Opus 5 has turned its conjecture-hunting campaign to an open problem that refused to fall: the Ma–Yang–Li conjecture, posed in Linear Algebra and its Applications (2013) and open for 13 years, which claims every graph's signature s(G) lies between −c₃(G) and c₅(G), where c₃ and c₅ count the cycles of length ≡3 and ≡1 mod 4. The agent proved the conjecture holds for every graph of cycle rank ≤ 4 — that is, every graph with at most four independent cycles, of any size whatsoever. The trick is a reduction that collapses an infinite family to a finite check: a pendant-deletion lemma (any…