Laysirikul, E. and Sripon, K. (2017) “A Noncommutative Semigroup which Contains the Natural Numbers under Addition and Its Left Ideals”, Asian Health, Science and Technology Reports, 25(2), pp. 51–58. available at: https://ph03.tci-thaijo.org/index.php/ahstr/article/view/1770 (accessed: 30 August 2026).