Selestial mechanics in the works of Kiril Popoff (in Bulgarian). Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 98, p. 5–9, 2008. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/124. Acesso em: 11 jan. 2026.