Awal, T., M. Mahbubuzzaman, and M. A. Kashem. “Algorithms for Finding Generalized Coloring of Trees”. INFOCOMP Journal of Computer Science, vol. 10, no. 1, Mar. 2011, pp. 36-44, https://infocomp.dcc.ufla.br/index.php/infocomp/article/view/326.