SHARA, J. On Free ɼ-Semigroups. International Journal For Research In Mathematics And Statistics, [S. l.], v. 3, n. 5, p. 01–14, 2017. DOI: 10.53555/ms.v3i5.229. Disponível em: https://ijfrms.com/index.php/ms/article/view/229. Acesso em: 15 jan. 2026.