TRUSCHINA, L. Über zweifache inhomogene Systeme von differentialgleischungen unendlicher Ordnung. Lithuanian Mathematical Journal, [S. l.], v. 11, n. 3, p. 691–703, 1971. DOI: 10.15388/LMJ.1971.21025. Disponível em: https://www.zurnalai.vu.lt/LMJ/article/view/21025. Acesso em: 3 may. 2025.