diff --git a/FormalConjectures/ErdosProblems/944.lean b/FormalConjectures/ErdosProblems/944.lean index 73c90ef0aa..3e9a47905e 100644 --- a/FormalConjectures/ErdosProblems/944.lean +++ b/FormalConjectures/ErdosProblems/944.lean @@ -110,4 +110,32 @@ theorem erdos_944.variants.large_k_for_any_r (r : ℕ) (hr : 1 ≤ r) : ∀ᶠ k ∃ (V : Type u) (G : SimpleGraph V), G.IsErdos944 k r := by sorry - end Erdos944 +/- +## Verified partial result for the $k = 4$, $r = 1$ case (6-regular subproblem) + +Skottová and Steiner [SkSt25] proved that every $(4,1)$-graph (a $4$-vertex-critical graph with +no critical edge) has minimum degree and edge-connectivity at least $6$, and asked (their +Problem 5.2) whether a $6$-regular $(4,1)$-graph exists. A verified computational programme [Fe26] +shows that there is no $6$-regular $4$-vertex-critical graph on $n \le 15$ except a unique one on +$n = 13$ (which has critical edges); hence any $6$-regular $(4,1)$-graph has at least $16$ +vertices. + +[SkSt25] Skottová, Ema and Steiner, Raphael, _Critical edge sets in vertex-critical graphs_, +arXiv:2508.08703 (2025). + +[Fe26] Ferudun, A., _Exact $6$-cut rigidity and small-order superconnectivity for the $6$-regular +case of Dirac's $k = 4$ problem_, arXiv:2606.18462 (2026). The full proofs, code, certificates, +and Lean cores are provided there. +-/ + +/-- Any $6$-regular $(4,1)$-graph — a $6$-regular $4$-vertex-critical graph with no critical +edge — has at least $16$ vertices: a verified computation [Fe26] rules out every such graph on +$n \le 15$, settling the small-order cases of Skottová–Steiner Problem 5.2 [SkSt25]. -/ +@[category research solved, AMS 5] +theorem erdos_944.variants.dirac_conjecture.k_eq_four.six_regular_min_order + [Fintype V] (G : SimpleGraph V) [DecidableRel G.Adj] + (hreg : G.IsRegularOfDegree 6) (h : G.IsErdos944 4 1) : + 16 ≤ Fintype.card V := by + sorry + +end Erdos944