Shkіl N. I. On the asymptotic solution of a system of partial linear differential equations . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 6, p. 85–96, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8461. Acesso em: 6 dec. 2025.