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Frederik Kortlandt, 'Glottalic Consonants in Sindhi and Proto-Indo-European', reprinted in Studies in Germanic, Indo-European, and Indo-Uralic, Amsterdam: Rodopi (2010), pp. 121-124. Counterarguments exist for his argument of no discernible substrate influence on the development of the specific Sindhi glottalization.[clarification needed] See also Michael Witzel, "Substrate Languages in Old Indo-Aryan", Electronic Journal of Vedic Studies 1999 (http://www.ejvs.laurasianacademy.com/ejvs0501/0501ART.PDFArchived 2013-09-21 at the Wayback Machine).
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