English

Excluded minors are almost fragile II: essential elements

Combinatorics 2023-09-07 v2

Abstract

Let MM be an excluded minor for the class of P\mathbb{P}-representable matroids for some partial field P\mathbb{P}, let NN be a 33-connected strong P\mathbb{P}-stabilizer that is non-binary, and suppose MM has a pair of elements {a,b}\{a,b\} such that M\a,bM\backslash a,b is 33-connected with an NN-minor. Suppose also that E(M)E(N)+11|E(M)| \geq |E(N)|+11 and M\a,bM \backslash a,b is not NN-fragile. In the prequel to this paper, we proved that M\a,bM \backslash a,b is at most five elements away from an NN-fragile minor. An element ee in a matroid MM' is NN-essential if neither M/eM'/e nor M\eM' \backslash e has an NN-minor. In this paper, we prove that, under mild assumptions, M\a,bM \backslash a,b is one element away from a minor having at least r(M)2r(M)-2 elements that are NN-essential.

Cite

@article{arxiv.2206.13036,
  title  = {Excluded minors are almost fragile II: essential elements},
  author = {Nick Brettell and James Oxley and Charles Semple and Geoff Whittle},
  journal= {arXiv preprint arXiv:2206.13036},
  year   = {2023}
}

Comments

34 pages, 2 figures

R2 v1 2026-06-24T12:04:42.778Z