PARASYUK, L. S. Generalized fundamental elliptical systems of differentia equations with discontinuous coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 18, n. 4, p. 124–126, 1966. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8322. Acesso em: 14 apr. 2025.