Kubichka, A. A., and I. O. Parasyuk. 2001. “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 (5), 610-24. https://umj.imath.kiev.ua/index.php/umj/article/view/4284.