@article{Duval:2011,
  author  = "G. Duval and A. Maciejewski",
  title   = "Taylor obstruction to the integrability of homogenous potentials of degree two. An application of higher order variational equations",
  journal = "Banach Center Publication : Algebraic methods in dynamical systems",
  volume  = "Vol. 94",
  pages   = "173--185",
  year    = "2011",
  note    = "Instytut Matematyczny PAN, Warszawa",
}