WANNUSIT, S.; PATTHANANGKOOR, P. On Semipolygroups. Thai Journal of Science and Technology, Pathumthani, Thailand, v. 7, n. 5, p. 443–451, 2018. DOI: 10.14456/tjst.2018.41. Disponível em: https://li01.tci-thaijo.org/index.php/tjst/article/view/139813. Acesso em: 5 dec. 2022.