English

On generalized list $\G$-free colorings of graphs

Combinatorics 2022-01-19 v1

Abstract

For given graph HH and graphical property PP, the conditional chromatic number χ(H,P)\chi(H,P) of HH, is the smallest number kk, so that V(H)V(H) can be decomposed into sets V1,V2,,VkV_1,V_2,\ldots, V_k, in which H[Vi]H[V_i] satisfies the property PP, for each 1ik1\leq i\leq k. When property PP be that each color class contains no copy of GG, we write χG(H)\chi_{G}(H) instead of χ(G,P)\chi(G,P), which is called the GG-free chromatic number. Due to this, we say HH has a kk-GG-free coloring if there is a map c:V(H){1,,k}c : V(H) \longrightarrow \{1,\ldots,k\}, so that each of the color classes of cc be GG-free. Assume that for each vertex vv of a graph HH is assigned a set L(V)L(V) of colors, called a color list. Set g(L)={g(v):vV(H)}g(L) = \{g(v): v\in V(H)\}, that is the set of colors chosen for the vertices of HH under gg. An LL-coloring gg is called GG-free, so that: \begin{itemize} \item g(v)L(v)g(v)\in L(v), for any vV(H)v\in V(H). \item H[Vi] H[V_i] is GG-free for each i=1,2,,Li=1,2,\ldots, L. \end{itemize} If there exists an LL-coloring of HH, then HH is called LL-GG-free-colorable. A graph HH is said to be kk-GG-free-choosable if there exists an LL-coloring for any list-assignment LL satisfying L(V)k|L(V)|\geq k for each vV(H)v\in V(H), and H[Vi]H[V_i] be GG-free for each i=1,2,,Li=1,2,\ldots, L. Let graph HH and a collection of graphs \G\G are given, the χ\GL(H)\chi_{\G}^L(H) of HH is the last integer kk, so that HH is kk-\G\G-free-choosable i.e. H[Vi]H[V_i] is \G\G-free for each i=1,2,,ki=1,2,\ldots, k i.e. contains no copy of any member of \G\G. In this article, we show that χGL(H)=χG(H)\chi_G^L(H)=\chi_G(H) for some graph HH and GG, χGL(HH)χGL(H)+χGL(H)\chi_G^L(H\oplus H')\leq \chi_G^L(H)+\chi_G^L(H') for each GG, HH, and HH'. Also, we show that χ\G(HKn)=χ\GL(HKn)\chi_{\G}(H\oplus K_n)=\chi^L_{\G}(H\oplus K_n), where \G\G is a collection of all dd-regular graphs, and some nn.

Keywords

Cite

@article{arxiv.2201.06029,
  title  = {On generalized list $\G$-free colorings of graphs},
  author = {Yaser Rowshan},
  journal= {arXiv preprint arXiv:2201.06029},
  year   = {2022}
}