HOROZOV, E. Selestial mechanics in the works of Kiril Popoff (in Bulgarian). Ann. Sofia Univ. Fac. Math. and Inf., [S. l.], v. 98, p. 5–9, 2008. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/124. Acesso em: 18 apr. 2025.