Courcelle, B., and V. Dussaux. “Map Genus, Forbidden Maps, and Monadic Second-Order Logic”. The Electronic Journal of Combinatorics 9, no. 1 (June 8, 2002): R40. Accessed March 15, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v9i1r40.