Haacke 2009 Haacke, W.H.G. (2009). "Khoesaan Languages". In Brown, Keith; Ogilvie, Sarah (eds.). Concise Encyclopedia of Languages of the World. Oxford, UK: Elsevier. pp. 600–602. ISBN9780080877747. LCCN2008934269.
Doke 1926 Doke, Clement Martyn (July 1926). "The Phonetics of the Zulu Language". Bantu Studies. 2. Johannesburg, South Africa: University of the Witwatersrand Press. ISSN0256-1751.