Li, Wei Qi, Li, Jin Bo, Miao, Lian Ying, and Song, Wen Yao. “On R-Hued Coloring of Planar Graphs With Girth at Least 5”. Utilitas Mathematica, vol. 109, Nov. 2018, https://utilitasmathematica.com/index.php/Index/article/view/1280.