van der Auwera, Johan, Lejeune, Ludo, Pappuswamy, Umarani, Goussev, Valentin. 2013 
The Morphological Imperative. Dryer, Matthew S., Haspelmath, Martin (eds.) 
The World Atlas of Language Structures Online Leipzig: Max Planck Institute for Evolutionary Anthropology. URL (Accessed on 2014-01-05.)