LAYSIRIKUL, E.; SRIPON, K. A Noncommutative Semigroup which Contains the Natural Numbers under Addition and Its Left Ideals. Asian Health, Science and Technology Reports, [S. l.], v. 25, n. 2, p. 51–58, 2017. Disponível em: https://ph03.tci-thaijo.org/index.php/ahstr/article/view/1770. Acesso em: 30 aug. 2026.