A further extension of R\"odl's theorem
Abstract
Fix and a nonnull graph . A well-known theorem of R\"odl from the 80s says that every graph with no induced copy of contains a linear-sized -restricted set , which means induces a subgraph with maximum degree at most in or its complement. There are two extensions of this result: quantitatively, Nikiforov (and later Fox and Sudakov) relaxed the condition "no induced copy of " into "at most induced copies of for some depending on and "; and qualitatively, Chudnovsky, Scott, Seymour, and Spirkl recently showed that there exists depending on and such that is -restricted, which means has a partition into at most subsets that are -restricted. A natural common generalization of these two asserts that every graph with at most induced copies of is -restricted for some depending on and . This is unfortunately false, but we prove that for every , and still exist so that for every , every graph with at most induced copies of has an -restricted induced subgraph on at least vertices. This unifies the two aforementioned theorems, and is optimal up to and for every value of .
Keywords
Cite
@article{arxiv.2208.07483,
title = {A further extension of R\"odl's theorem},
author = {Tung H. Nguyen},
journal= {arXiv preprint arXiv:2208.07483},
year = {2023}
}
Comments
11 pages, revised according to the referees' comments