Ranko Matasović (2007). "Insular Celtic as a Language Area". In Tristram, Hildegard L.C. (ed.). The Celtic Languages in Contact Papers from the Workshop Within the Framework of the XIII International Congress of Celtic Studies, Bonn, 26-27 July 2007. Bonn: Potsdam University Press. p. 108. ISBN9783940793072. Retrieved 18 August 2022.
jstor.org
David Greene (1976). "The Diphthongs of Old Irish". Ériu. 27: 26–45. JSTOR30007667.