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

preprint2022arXivOpen access

Abstract

For given graph HH and graphical property PP, the conditional chromatic number χ(H,P)χ(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 1≤i≤k1\leq i\leq k. When property PP be that each color class contains no copy of GG, we write χG(H)χ_{G}(H) instead of χ(G,P)χ(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):v∈V(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 v∈V(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 v∈V(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 $\G$ are given, the $χ_{\G}^L(H)$ of HH is the last integer kk, so that HH is kk-$\G$-free-choosable i.e. H[Vi]H[V_i] is $\G$-free for each i=1,2,…,ki=1,2,\ldots, k i.e. contains no copy of any member of $\G$. In this article, we show that χGL(H)=χG(H)χ_G^L(H)=χ_G(H) for some graph HH and GG, χGL(H⊕H′)≤χGL(H)+χGL(H′)χ_G^L(H\oplus H')\leq χ_G^L(H)+χ_G^L(H') for each GG, HH, and H′H'. Also, we show that $χ_{\G}(H\oplus K_n)=χ^L_{\G}(H\oplus K_n)$, where $\G$ is a collection of all dd-regular graphs, and some nn.

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