“A Geometrical Generalization of the Poincaré Method for an Investigation of Lagrangian Manifolds of Slowly Perturbed Hamiltonian Systems in a Neihborhood of a Hyperbolic Singular Point”. 2000. Neliniini Kolyvannya 3 (2): 246-55. https://twinhead.imath.kiev.ua/index.php/nosc/article/view/114.