English

Ramsey numbers for trees II

Combinatorics 2023-02-17 v5

Abstract

Let r(G1,G2)r(G_1, G_2) be the Ramsey number of the two graphs G1G_1 and G2G_2. For n1n21n_1\ge n_2\ge 1 let S(n1,n2)S(n_1,n_2) be the double star given by V(S(n1,n2))={v0,v1,,vn1,w0,w1,,wn2}V(S(n_1,n_2))=\{v_0,v_1,\ldots,v_{n_1},w_0,w_1,\ldots,w_{n_2}\} and E(S(n1,n2))={v0v1,,v0vn1,v0w0,w0w1,,w0wn2}E(S(n_1,n_2))=\{v_0v_1,\ldots,v_0v_{n_1},v_0w_0,w_0w_1,\ldots,w_0w_{n_2}\}. In this paper we determine r(K1,m1,r(K_{1,m-1}, S(n1,n2))S(n_1,n_2)) under certain conditions. For n6n\ge 6 let Tn3=S(n5,3)T_n^3=S(n-5,3), Tn=(V,E2)T_n^{''}=(V,E_2) and Tn=(V,E3)T_n^{'''} =(V,E_3), where V={v0,v1,,vn1}V=\{v_0,v_1,\ldots,v_{n-1}\}, E2={v0v1,,v0vn4,v1vn3,v1vn2,E_2=\{v_0v_1,\ldots,v_0v_{n-4},v_1v_{n-3},v_1v_{n-2}, v2vn1}v_2v_{n-1}\} and E3={v0v1,,v0vn4,v1vn3,v2vn2,v3vn1}E_3=\{v_0v_1,\ldots,v_0v_{n-4},v_1v_{n-3},v_2v_{n-2},v_3v_{n-1}\}. We also obtain explicit formulas for rr (K1,m1,Tn)(K_{1,m-1},T_n), r(Tm,Tn)r(T_m',T_n) (nm+3)(n\ge m+3), r(Tn,Tn)r(T_n,T_n), r(Tn,Tn)r(T_n',T_n) and r(Pn,Tn)r(P_n,T_n), where Tn{Tn,Tn,Tn3}T_n\in\{T_n'',T_n''',T_n^3\}, PnP_n is the path on nn vertices and TnT_n' is the unique tree with nn vertices and maximal degree n2n-2.

Keywords

Cite

@article{arxiv.1410.7637,
  title  = {Ramsey numbers for trees II},
  author = {Zhi-Hong Sun},
  journal= {arXiv preprint arXiv:1410.7637},
  year   = {2023}
}

Comments

25 pages (published version)

R2 v1 2026-06-22T06:38:44.472Z