The exceptional-graph conjecture for local antimagic chromatic number

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Let GG be a graph with k1k\ge 1 pendant vertices and chromatic number χ(G)\chi(G) satisfying kχ(G)1k\ge \chi(G)-1. The graphs K(2;a,b)K(2;a,b), caterpillar graphs in the cited theorem, Ct(3;n1,0,n3)Ct(3;n_1,0,n_3), and the indicated corona graphs PmOnP_m\odot O_n, CmOnC_m\odot O_n, and KmOnK_m\odot O_n are defined by the displayed exceptional conditions. Exceptional-graph conjecture. All graphs GG with kχ(G)1k\ge\chi(G)-1 pendants have χla(G)=k+1\chi_{la}(G)=k+1, except the following cases: χla(K(2;a,b))=a+b+2\chi_{la}(K(2;a,b))=a+b+2 for ab2a\ge b\ge2 and a<b(b+1)/2a<b(b+1)/2; the caterpillar graphs in Theorem~; χla(Ct(3;n1,0,n3))=n1+n3+2\chi_{la}(Ct(3;n_1,0,n_3))=n_1+n_3+2 under the stated inequalities and congruence condition; and the three stated corona families with their displayed values or lower bound. This is presented as a proposed global classification; no resolution is supplied in the paper.

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Primary source

Gee-Choon Lau, Wai-Chee Shiu and Ho-Kuen Ng, “On number of pendants in local antimagic chromatic number”, arXiv:2001.05138 (2020).

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