@article{Maciejewski:2008,
  author  = "A. Maciejewski and M. Przybylska and H. Yoshida",
  title   = "Necessary conditions for super-integrability of Hamiltonian systems",
  journal = "Physics Letters A",
  volume  = "Vol. 372",
  number  = "no 34",
  pages   = "5581--5587",
  year    = "2008",
}