SAKHNOVICH , L. A. Evolution of spectral data and nonlinear equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 4, p. 533–535, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9195. Acesso em: 7 dec. 2025.