Stojkovikj, Natasha, Mirjana Kocaleva, Cveta Martinovska Bande, Aleksandra Stojanova, & Biljana Zlatanovska. " Application of the Four-Color Theorem for coloring a city map." Balkan Journal of Applied Mathematics and Informatics [Online], 3.1 (2020): pp. 25-36. Web. 13 Aug. 2020