@article{Matkowski:1998,
  author  = "J. Matkowski and T. Zgraja",
  title   = "A separation theorem for M -convex functions",
  journal = "Mathematica Pannonica",
  volume  = "Vol. 9",
  number  = "no 1",
  pages   = "103--109",
  year    = "1998",
}