English

Elastic elements in 3-connected matroids

Combinatorics 2021-11-24 v3

Abstract

It follows by Bixby's Lemma that if ee is an element of a 33-connected matroid MM, then either co(M\deletee){\rm co}(M\delete e), the cosimplification of M\deleteeM\delete e, or si(M/e){\rm si}(M/e), the simplification of M/eM/e, is 33-connected. A natural question to ask is whether MM has an element ee such that both co(M\deletee){\rm co}(M\delete e) and si(M/e){\rm si}(M/e) are 33-connected. Calling such an element "elastic", in this paper we show that if E(M)4|E(M)|\ge 4, then MM has at least four elastic elements provided MM has no 44-element fans and, up to duality, MM has no 33-separating set SS that is the disjoint union of a rank-22 subset and a corank-22 subset of E(M)E(M) such that MSM|S is isomorphic to a member or a single-element deletion of a member of a certain family of matroids.

Cite

@article{arxiv.2010.01797,
  title  = {Elastic elements in 3-connected matroids},
  author = {George Drummond and Zachary Gershkoff and Susan Jowett and Charles Semple and Jagdeep Singh},
  journal= {arXiv preprint arXiv:2010.01797},
  year   = {2021}
}

Comments

20 pages, 1 figure. The main result (Theorem 1) in the original paper is incorrect. In particular, as well as 4-element fans, there is also a family of exceptions. An error in one of the earlier lemmas was missed. We have corrected the paper

R2 v1 2026-06-23T19:01:50.349Z