“Bifurcation of Coisotropic Invariant Tori under Locally Hamiltonian Perturbations of Integrable Systems and Nondegenerate Deformations of the Symplectic Structure”. Neliniini Kolyvannya, vol. 9, no. 2, June 2006, pp. 221-32, https://twinhead.imath.kiev.ua/index.php/nosc/article/view/393.