English

Ramsey sequences with bounded clique size

Combinatorics 2025-09-30 v1

Abstract

A sequence of graphs {Gk} \{G_k\} is a Ramsey sequence if for every positive integer k k , the graph Gk G_k is a proper subgraph of Gk+1 G_{k+1} , and there exists an integer n>kn > k such that every red-blue coloring of Gn G_n contains a monochromatic copy of Gk G_k . Among the wide range of open problems in Ramsey theory, an interesting open question is ``Does there exist an ascending sequence {Gk}\{G_k\} with limkχ(Gk)=\lim_{k \to \infty} \chi(G_k) = \infty and limkω(Gk)\lim_{k \to \infty} \omega(G_k) \neq \infty that is a Ramsey sequence?". In this paper, we solve this problem by constructing a Ramsey sequence {Gk}\{G_k\} with a bounded clique number such that limkχ(Gk)=\lim_{k \to \infty} \chi(G_k) = \infty. Furthermore, using the observation that any monotonic increasing sequence of graphs that contains a Ramsey sequence as a subgraph is also Ramsey, we can generate infinitely many Ramsey sequences using this example.

Keywords

Cite

@article{arxiv.2509.23929,
  title  = {Ramsey sequences with bounded clique size},
  author = {Abhishek Girish Aher and Aparna Lakshmanan S},
  journal= {arXiv preprint arXiv:2509.23929},
  year   = {2025}
}
R2 v1 2026-07-01T06:02:45.108Z