Laysirikul, Ekkachai, Nares Sawatraksa, and Chaiwat Namnak. “Left regular and right regular elements of the semigroups of transformations restricted by an equivalence”. Asian Health, Science and Technology Reports 26, no. 4 (November 15, 2018): 89–93. accessed August 30, 2026. https://ph03.tci-thaijo.org/index.php/ahstr/article/view/1638.