Sripon, K., E. Laysirikul, and Y. Chaiya. “A Note on Regularity of Certain Semigroups of Transformations Preserving a Reflexive and Transitive Relation”. Science & Technology Asia, vol. 28, no. 3, Sept. 2023, pp. 37-43, https://ph02.tci-thaijo.org/index.php/SciTechAsia/article/view/248936.