I. O. Parasyuk, “Variables of the action-angle type on symplectic manifolds stratified by coisotropic tori”, Ukr. Mat. Zhurn., vol. 45, no. 1, pp. 77–85, Jan. 1993, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5785