ParasyukI. O. 1994. “Reduction and Coisotropic Invariant Tori of Hamiltonian Systems With Non-Poisson Commutative Symmetries. I”. Ukrains’kyi Matematychnyi Zhurnal 46 (5), 537–544. https://umj.imath.kiev.ua/index.php/umj/article/view/5717.