Comparison principle for linear non-cooperative elliptic systems. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 99, p. 111–119, 2009. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/115. Acesso em: 15 dec. 2025.