@InCollection{Porcu:2008,
  author    = "E. Porcu and J. Matkowski and J. Mateu",
  title     = "Quasi arithmetic covariance functions and their possible reducibility through functional equations",
  pages     = "155--180",
  year      = "2008",
  booktitle = "Positive definite functions: from Schoenberg to space-time challenges, ISBN: 9788461282821",
  editor    = "ed. J. Mateu, E. Porcu",
  publisher = "Publications de la Universitat Jaume I",
  address   = "Castelló de la Plana",
}