REK, Stanisław. The genesis of the tsar title in the West-Bulgarian state. Balcanica Posnaniensia. Acta et studia, [S. l.], v. 2, p. 51–58, 1985. DOI: 10.14746/bp.1985.2.5. Disponível em: https://pressto.amu.edu.pl/index.php/bp/article/view/54816. Acesso em: 4 oct. 2026.