Fleischner, Herbert J., Dennis P. Geller, and Frank Harary. “Outerplanar Graphs and Weak Duals”. The Journal of the Indian Mathematical Society 38, no. 1-4 (December 1, 1974): 215–219. Accessed April 19, 2024. https://informaticsjournals.com/index.php/jims/article/view/16694.