English

Halfway to induced saturation for even cycles

Combinatorics 2025-06-03 v2

Abstract

For graphs GG and HH, we say that GG is HH-free if no induced subgraph of GG is isomorphic to HH, and that GG is HH-induced-saturated if GG is HH-free but removing or adding any edge in GG creates an induced copy of HH. A full characterization of graphs HH for which HH-induced-saturated graphs exist remains elusive. Even the case where HH is a path -- now settled by the collective results of Martin and Smith, Bonamy et al., and Dvo\'{r}\v{a}k -- was already quite challenging. What if HH is a cycle? The complete answer for odd cycles was given by Behren et al., leaving the case of even cycles (except for the 44-cycle) wide open. Our main result is the first step toward closing this gap: We prove that for every even cycle HH, there is a graph GG with at least one edge such that GG is HH-free but removing any edge from GG creates an induced copy of HH (in fact, we construct HH-induced-saturated graphs for every even cycle HH on at most 10 vertices).

Keywords

Cite

@article{arxiv.2505.24100,
  title  = {Halfway to induced saturation for even cycles},
  author = {Xinyue Fan and Sahab Hajebi and Sepehr Hajebi and Sophie Spirkl},
  journal= {arXiv preprint arXiv:2505.24100},
  year   = {2025}
}
R2 v1 2026-07-01T02:49:39.925Z