@article{Baksalary:2006,
  author  = "O. Baksalary and P. Kik",
  title   = "On commutativity of projectors",
  journal = "Linear Algebra and its Applications",
  volume  = "Vol. 417",
  number  = "no 1",
  pages   = "31--41",
  year    = "2006",
}