DEGREE SPECTRA AND CO-SPECTRA OF STRUCTURES. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 96, p. 45–68, 2004. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/160. Acesso em: 11 jan. 2026.