However, the posited Tlapanec case system is verbal, and it is controversial whether verbal case as such actually exists.
- Wichmann, Søren (2005). "Tlapanec Cases" (PDF). In Rosemary Beam de Azcona and Mary Paster (eds.). Report 13, Survey of California and Other Indian Languages. Conference on Otomanguean and Oaxacan Languages, March 19–21, 2004. Berkeley CA: University of California at Berkeley. pp. 133–145. Archived from the original on November 2, 2014. Retrieved 2011-03-01.