Güldemann, Tom (2018). "Historical linguistics and genealogical language classification in Africa". In Güldemann, Tom (ed.). The Languages and Linguistics of Africa. The World of Linguistics series. Vol. 11. Berlin: De Gruyter Mouton. pp. 58–444. doi:10.1515/9783110421668-002. ISBN978-3-11-042606-9. S2CID133888593.
Güldemann, Tom (2018). "Historical linguistics and genealogical language classification in Africa". In Güldemann, Tom (ed.). The Languages and Linguistics of Africa. The World of Linguistics series. Vol. 11. Berlin: De Gruyter Mouton. pp. 58–444. doi:10.1515/9783110421668-002. ISBN978-3-11-042606-9. S2CID133888593.
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Rolf Theil (2006) Is Omotic Afro-Asiatic? pp 1–2: "I claim to show that no convincing arguments have been presented [for the inclusion of Omotic (OM) in Afro-Asiatic (AA)], and that OM should be regarded as an independent language family. No closer genetic relations have been demonstrated between OM and AA than between OM and any other language family."