Kubichka, A. A., and I. O. Parasyuk. “Bifurcation of a Whitney-Smooth Family of Coisotropic Invariant Tori of a Hamiltonian System under Small Deformations of a Symplectic Structure”. Ukrains’kyi Matematychnyi Zhurnal 53, no. 5 (May 25, 2001): 610–624. Accessed April 27, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4284.