@article{Matkowski:2002,
  author  = "J. Matkowski and W. Slepak",
  title   = "On (\alfa, a)-convex set-valued functions",
  journal = "Far East Journal of Mathematical Sciences",
  volume  = "Vol. 4",
  number  = "no 1",
  pages   = "85--89",
  year    = "2002",
}