Kerdjoudj, Samia, Chaouche, Fatima Affif, and Berrachedi, Abdelhafid. “The 6-Coloring and 6-Continuity of the Cartesian Product of Some Graphs”. Utilitas Mathematica, vol. 104, Sept. 2017, https://utilitasmathematica.com/index.php/Index/article/view/1204.