English

How Ramsey theory can be used to solve Harary's problem for $K_{2,k}$

Combinatorics 2019-01-08 v1

Abstract

Harary's conjecture r(C3,G)2q+1r(C_3,G)\leq 2q+1 for every isolated-free graph G with qq edges was proved independently by Sidorenko and Goddard and Klietman. In this paper instead of C3C_3 we consider K2,kK_{2,k} and seek a sharp upper bound for r(K2,k,G)r(K_{2,k},G) over all graphs GG with qq edges. More specifically if q2q\geq 2, we will show that r(C4,G)kq+1r(C_4,G)\leq kq+1 and that equality holds if GqK2G \cong qK_2 or K3K_3. Using this we will generalize this result for r(K2,k,G)r(K_{2,k},G) when k>2k>2. We will also show that for every graph GG with q2q \geq 2 edges and with no isolated vertices, r(C4,G)2p+q2r(C_4, G) \leq 2p+ q - 2 where p=V(G)p=|V(G)| and that equality holds if GK3G \cong K_3.

Keywords

Cite

@article{arxiv.1901.01552,
  title  = {How Ramsey theory can be used to solve Harary's problem for $K_{2,k}$},
  author = {C. J. Jayawardene and C. C. Rousseau and B. Bollobás},
  journal= {arXiv preprint arXiv:1901.01552},
  year   = {2019}
}

Comments

8 pages, 4 figures