Бројевни систем — разлика између измена

* A. L. Kroeber (Alfred Louis Kroeber) (1876–1960), Handbook of the Indians of California, Bulletin 78 of the Bureau of American Ethnology of the Smithsonian Institution (1919)

* J.P. Mallory and D.Q. Adams, ''Encyclopedia of Indo-European Culture'', Fitzroy Dearborn Publishers, London and Chicago, 1997.

* {{Cite book| ref = harv | last = Zaslavsky | first = Claudia |title=Africa Counts: Number and Pattern in African Cultures|location=|publisher=Lawrence Hill Books|year=1999|isbn=978-1-55652-350-2|pages=}}.

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