Heikkinen, Terttu. 1986. "Phonology of the !Xũ Dialect Spoken in Ovamboland and Western Kavango." In South African Journal of African Languages, 6 , no. 1: 18-28.
Hayward, Richard J. 1990. "Notes On the Zayse Language." In Omotic Language Studies, edited by Richard J. Hayward. 210-355. School of Oriental and African Studies.
Hayward, Richard J. 1978. "The Qawko Dialects and Yaaku." In Abbay: Documents pour Servir à la histoire de la Civilisation Éthiopienne. Cahier n, 9: 59-70.