Various memories of Rumen Maleev - the colleague and friend. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 107, p. 9–13, 2020. DOI: 10.60063/gsu.fmi.107.9-13. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/102. Acesso em: 16 dec. 2025.