ROMANOV, S. S. Plane Closed Trajectories on Certain Manifolds with Rotation Metric. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 56, n. 2, p. 276–283, 2004. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3752. Acesso em: 6 dec. 2025.