↑Mallory J.P. & Adams D.Q. 2006. The Oxford introduction to Proto-Indo-European and the Proto-Indo-European world. Oxford: Oxford University Press. ISBN0-19-929668-5
↑Ivanov, Vyacheslav V.& Gamkrelidze, Thomas 1990. The early history of Indo-European languages. Scientific American262, March.
↑Beekes Robert 1995. Comparative Indo-European linguistics: an introduction. Amsterdam: John Benjamins. ISBN90-272-2150-2 (Europe), ISBN1-55619-504-4 (US)