DREWNIAK, J.; DUDZIAK, U. Aggregations in classes of fuzzy relations. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 5, p. 33–43, 2006. Disponível em: https://studmath.uken.krakow.pl/article/view/13290. Acesso em: 31 oct. 2026.