ÉSIK, Zoltán. Free De Morgan Bisemigroups and Bisemilattices. BRICS Report Series, [S. l.], v. 8, n. 38, 2001. DOI: 10.7146/brics.v8i38.21698. Disponível em: https://tidsskrift.dk/brics/article/view/21698. Acesso em: 6 dec. 2025.