NAGY, Attila. REFLEXIVE UNITARY SUBSEMIGROUPS OF LEFT SIMPLE SEMIGROUPS Periodica Polytechnica Transportation Engineering, [S. l.], v. 19, n. 1-2, p. 61–69, 1991. Disponível em: https://pp.bme.hu/tr/article/view/6684. Acesso em: 16 may. 2025.