Circular consecutive choosability of k-choosable graphs

100學年度研究獎補助論文[[abstract]]Let S(r) denote a circle of circumference r. The circular consecutive choosability chcc(G) of a graph G is the least real number t such that for any r≥χc(G), if each vertex v is assigned a closed interval L(v) of length t on S(r), then there is a circular r-coloring f of G such that f(v)∈L(v). We investigate, for a graph, the relations between its circular consecutive choosability and choosability. It is proved that for any positive integer k, if a graph G is k-choosable, then chcc(G)≦k + 1 − 1/k; moreover, the bound is sharp for k≥3. For k = 2, it is proved that if G is 2-choosable then chcc(G)≦2, while the equality holds if and only if G contains a cycle. In addition, we prove that there exist circular consecutive 2-choosable graphs which are not 2-choosable. In particular, it is shown that chcc(G) = 2 holds for all cycles and for K2, n with n≥2. On the other hand, we prove that chcc(G)＞2 holds for many generalized theta graphs.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[booktype]]電子版[[countrycodes]]US