@article{Matkowski:2007,
  author  = "J. Matkowski",
  title   = "When M-convexity of a function implies its N-convexity for some means M and N",
  journal = "International Mathematical Forum",
  volume  = "Vol. 47",
  number  = "no 2",
  pages   = "2321--2331",
  year    = "2007",
}