Arno Borst, Medieval Worlds : Barbarians, Heretics, and Artists in the Middle Ages, University of Chicago, 1992, (ISBN0-226-06656-8), p. 132.
Cette expression est utilisée pour la première fois dans l'Historia Norwegiæ contemporaine- Knut Helle, The Cambridge History of Scandinavia Volume 1, Prehistory to 1520, Cambridge University Press, 2003, (ISBN0-521-47299-7), p. 379.
genealogi.no
Jo Rune Ugulen, "Kongar i dei norske ættetavlene" (Kings in the Norwegian genealogies), Norsk Slektshistorisk Forening 1999/2000, reprinted from Genealogen 99.1, p. 20-23
