PROPERTIES OF CO-SPECTRA OF JOINT SPECTRA OF STRUCTURES. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 97, p. 23–40, 2005. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/142. Acesso em: 14 dec. 2025.