KOROBEINIK, J. Normally solvable operators and differential equations of infinite order. Lithuanian Mathematical Journal, [S. l.], v. 11, n. 3, p. 569–596, 1971. DOI: 10.15388/LMJ.1971.21016. Disponível em: https://www.journals.vu.lt/LMJ/article/view/21016.. Acesso em: 3 may. 2024.