Ljusternik-Schnirelman category of the non-wandering set. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 84, p. 43–48, 1993. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/466. Acesso em: 12 jan. 2026.