Abstract
We recently introduced proportional choosability, a new list analogue of equitable coloring. Like equitable coloring, and unlike list equitable coloring (a.k.a. equitable choosability), proportional choosability bounds sizes of color classes both from above and from below. In this note, we show that a graph is proportionally 2-choosable if and only if it is a linear forest such that its largest component has at most five vertices and all of its other components have two or fewer vertices. We also construct examples that show that characterizing equitably 2-choosable graphs is still open.
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The authors would like to thank the anonymous referees whose comments helped improve the readability of this note.
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Kaul, H., Mudrock, J.A., Pelsmajer, M.J. et al. A Simple Characterization of Proportionally 2-choosable Graphs. Graphs and Combinatorics 36, 679–687 (2020). https://doi.org/10.1007/s00373-020-02146-z
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DOI: https://doi.org/10.1007/s00373-020-02146-z