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Ethnologue: Languages of the World, 18th Edition . (2015) · edited by Lewis, M. Paul, Gary F. Simons, and Charles D. Fennig · SIL International http://www.ethnologue.com

Sepik languages: checklist and preliminary classification . Laycock, Donald C. (1973) · Pacific Linguistics · edited by Wurm, Stephen A. · Australian National University, Research School of Pacific Studies, Department of Linguistics

Glottolog 2.3 . Hammarström, Harald & Forkel, Robert & Haspelmath, Martin & Nordhoff, Sebastian (2014) · http://glottolog.org

Ethnologue: Languages of the World, 18th Edition . (2015) · edited by Lewis, M. Paul, Gary F. Simons, and Charles D. Fennig · SIL International http://www.ethnologue.com

Sepik languages: checklist and preliminary classification . Laycock, Donald C. (1973) · Pacific Linguistics · edited by Wurm, Stephen A. · Australian National University, Research School of Pacific Studies, Department of Linguistics

Glottolog 2.3 . Hammarström, Harald & Forkel, Robert & Haspelmath, Martin & Nordhoff, Sebastian (2014) · http://glottolog.org

A sociolinguistic survey of Heyo, Pahi, and Mayo-Pasi ( pp. 109-140 ) . Hutchinson, Ian Workpapers in Papua New Guinea Languages ·