SKRYPNIK, W. I. On the Evolution Operator of the Gradient Diffusion Hierarchy for Plane Rotators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 53, n. 12, p. 1664–1685, 2001. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4386. Acesso em: 11 apr. 2025.