Sankarnarayanan, Brahadeesh, and Niranjan Balachandran. “The Choice Number Versus the Chromatic Number for Graphs Embeddable on Orientable Surfaces”. The Electronic Journal of Combinatorics 28, no. 4 (December 17, 2021): P4.50. Accessed March 17, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v28i4p50.