DITCHEV, A. Examples of structures which do not admit recursive presentations. Ann. Sofia Univ. Fac. Math. and Inf., [S. l.], v. 85, p. 3–11, 1993. Disponível em: https://stipendii.uni-sofia.bg/index.php/fmi/article/view/448. Acesso em: 5 dec. 2024.