Eugen, Hill (2012). Hidden sound laws in the inflectional morphology of Proto-Indo-European. У Nielsen Whitehead, Benedicte; Olander, Thomas; Olsen, Birgit Anette; Rasmussen, Jens Elmegård (ред.). The Sound of Indo-European – Phonetics, Phonemics and Morphophonemics. Copenhagen: Museum Tusculanum Press. с. 190. Процитовано 11 жовтня 2015.
