Cycle lengths modulo k in large 3-connected cubic graphs

- DTU Compute, Technical University of Denmark

- DTU Compute, Technical University of Denmark
**ORCID iD:**0000-0003-4555-6021

### Editorial introduction

The existence of cycles of a prescribed length in graphs is a classical topic in graph theory with a plethora of open problems. Examples related to the main result of this paper include a conjecture of Burr and Erdős from 1976, which asks for every integer m and a positive odd integer k, there exists d such that every graph with average degree at least d contains a cycle of length m modulo k; this conjecture was proven by Bollobás in Bull. London Math. Soc. 9 (1977), 97-98. Another example is a problem of Erdős from the 1990s asking whether there exists A⊆N with zero density and constants n0 and d0 such that every graph with at least n0 vertices and the average degree at least d0 contains a cycle with length in the set A, which was resolved by Verstraete in J. Graph Theory 49 (2005), 151-167. In 1983, Thomassen conjectured that for all integers m and k, every graph with minimum degree k+1 contains a cycle of length 2m modulo k. Note that the parity condition in the first and the third conjectures is necessary because of bipartite graphs.

The current paper contributes to this long line of research by proving that for every integer m and a positive odd integer k, every sufficiently large 3-connected cubic graph contains a cycle of length m modulo k. The result is the best possible in the sense that the same conclusion is not true for 2-connected cubic graphs or 3-connected graphs with minimum degree three.