IL'KIV, V. S. A problem with formal initial conditions for differential equations with constant pseudodifferential coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 50, n. 7, p. 877–888, 1998. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4868. Acesso em: 14 apr. 2025.