English

Small 4-regular planar graphs that are not circle representable

Combinatorics 2019-08-14 v2

Abstract

A 4-regular planar graph GG is said to be circle representable if there exists a collection of circles drawn on the plane such that the touching and crossing points correspond to the vertices of GG, and the circular arcs between those points correspond to the edges of GG. Lov\'asz (1970) conjectured that every 4-regular planar graph has a circle representation, but an infinite family of counterexamples was given by Bekos and Raftopoulou (2015). We reduce the order of the smallest known counterexamples among simple graphs from 822 to 68 based on a multigraph counterexample of order 12.

Keywords

Cite

@article{arxiv.1902.01158,
  title  = {Small 4-regular planar graphs that are not circle representable},
  author = {Jane Tan},
  journal= {arXiv preprint arXiv:1902.01158},
  year   = {2019}
}

Comments

This version has changes to exposition and cleaner arguments

R2 v1 2026-06-23T07:31:20.868Z