^Geoffrey Sampson (1985). Writing Systems. Stanford University Press. pp. 80-81. ISBN0804717567
^Joseph Naveh (1987) [1982]. Early History of the Alphabet (2nd ed.). Hebrew University. p. 25. ISBN9652234362
^Peter T. Daniels (1996). “The First Civilizations”. In Peter T. Daniels; William Bright. The World's Writing Systems. Oxford University Press. p. 29. ISBN0195079930