FINKELSHTEIN, D. L. Around Ovsyannikov’s method. Methods of Functional Analysis and Topology, [S. l.], v. 21, n. 2, p. 134–150, 2015. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/607. Acesso em: 16 dec. 2025.