@article{Jankiewicz:2007,
  author  = "J. Jankiewicz and K. Urbanowski",
  title   = "On Khalfin's improvement of the LOY effective Hamiltonian for neutral meson complex",
  journal = "European Physical Journal C",
  volume  = "Vol. 49",
  pages   = "721--730",
  year    = "2007",
}