RYKHNLOV, V. Eigenfunction completeness for a third-order ordinary differential bundle of operators. Математическая физика, анализ, геометрия, Харків, Україна, v. 3, n. 3-4, p. 406–411, 1996. Disponível em: http://mag.ilt.kharkiv.ua/index.php/mag/article/view/m03-0406e. Acesso em: 19 трав. 2024.