Sen, B. K., W. K. Khong, S. H. Lee, B. L. Lim, M. R. Abdullah, C. N. Ting, and S. H. Wee. “ZIPF’S LAW AND WRITINGS ON LIS”. Malaysian Journal of Library and Information Science, vol. 3, no. 1, July 1998, pp. 93-98, http://ojie.um.edu.my/index.php/MJLIS/article/view/6652.