Atkinson, Q. D.; Nicholls, G.; Welch, D.; & Gray, R. D. (2005): Transactions of the Philological Society, 103(2), 193-219. Renfrew, Colin (1987): . London: Jonathan Cape. ISBN 0-224-02495-7 Sykes, Brian (2001): (London, Corgi Books) Watkins, Calvert (1995): . New York: Oxford University Press.