KEHAYOPULU, Niovi; TSINGELIS, Michael. Principal filters of some ordered $\Gamma$-semigroups. Armenian Journal of Mathematics, Yerevan, Armenia, v. 8, n. 2, p. 96–103, 2016. Disponível em: https://armjmath.sci.am/index.php/ajm/article/view/127. Acesso em: 3 apr. 2025.