Team, Support. “Regular Elements of Semigroups of Continuous Functions and Differentiable Functions: Y. Punkla, Y. Kemprasit, S. Nenthein”. Thai Journal of Mathematics 3, no. 2 (December 1, 2005): 137–144. Accessed May 2, 2024. https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/18.