Koike, Hiroki, Daniel Pellicer, Miguel Raggi, and Steve Wilson. “Flag Bicolorings, Pseudo-Orientations, and Double Covers of Maps”. The Electronic Journal of Combinatorics 24, no. 1 (January 20, 2017): P1.3. Accessed April 4, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v24i1p3.