GEORGIEV, G.; TINCHEV, T. Monadic second-order logic on equivalence relations. Ann. Sofia Univ. Fac. Math. and Inf., [S. l.], v. 99, p. 25–35, 2009. Disponível em: https://ftl5.uni-sofia.bg/index.php/fmi/article/view/110. Acesso em: 4 dec. 2024.