LOUKANOVA, R.; COOPER, R. Some situation theoretical notions. Ann. Sofia Univ. Fac. Math. and Inf., [S. l.], v. 87, p. 297–306, 1995. Disponível em: https://ftl5.uni-sofia.bg./index.php/fmi/article/view/423. Acesso em: 3 apr. 2025.