English

Absolutely avoidable order-size pairs for induced subgraphs

Combinatorics 2021-07-30 v2

Abstract

We call a pair (m,f)(m,f) of integers, m1m\geq 1, 0f(m2)0\leq f \leq \binom{m}{2}, \emph{absolutely avoidable} if there is n0n_0 such that for any pair of integers (n,e)(n,e) with n>n0n>n_0 and 0e(n2)0\leq e\leq \binom{n}{2} there is a graph on nn vertices and ee edges that contains no induced subgraph on mm vertices and ff edges. Some pairs are clearly not absolutely avoidable, for example (m,0)(m,0) is not absolutely avoidable since any sufficiently sparse graph on at least mm vertices contains independent sets on mm vertices. Here we show that there are infinitely many absolutely avoidable pairs. We give a specific infinite set MM such that for any mMm\in M, the pair (m,(m2)/2)(m, \binom{m}{2}/2) is absolutely avoidable. In addition, among other results, we show that for any monotone integer function q(m)q(m), q(m)=O(m)|q(m)|=O(m), there are infinitely many values of mm such that the pair (m,(m2)/2+q(m))(m, \binom{m}{2}/2 +q(m)) is absolutely avoidable.

Keywords

Cite

@article{arxiv.2106.14908,
  title  = {Absolutely avoidable order-size pairs for induced subgraphs},
  author = {Maria Axenovich and Lea Weber},
  journal= {arXiv preprint arXiv:2106.14908},
  year   = {2021}
}
R2 v1 2026-06-24T03:41:14.752Z