^Byrd, Andrew Miles (2015),The Indo-European Syllable (Brill's Studies in Indo-European Languages & Linguistics;15), Leiden: Brill, page259
^Kölligan, Daniel (2017–2018), “Chapter XX: Proto-Indo-European”, in Klein, Jared S.,Joseph, Brian D.,Fritz, Matthias, editors,Handbook of Comparative and Historical Indo-European Linguistics: An International Handbook (Handbücher zur Sprach- und Kommunikationswissenschaft[Handbooks of Linguistics and Communication Science];41.2), Berlin; Boston: De Gruyter Mouton,→ISBN, § The lexicon of Proto-Indo-European, page2258
^De Vaan, Michiel (2008), “ad”, inEtymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill,→ISBN,page24
↑7.07.1Garnier, Romain (2014), “Nouvelles réflexions sur l’effet-Kortlandt”, inGlotta[3] (in French), volume90, Vandenhoeck & Ruprecht, pages140-160
^Ačaṙean, Hračʻeay (1979), “ց”, inHayerēn armatakan baṙaran [Armenian Etymological Dictionary] (in Armenian), 2nd edition, a reprint of the original 1926–1935 seven-volume edition, volume IV, Yerevan: University Press,page446a
Andrew Byrd,The Indo-European Syllable (2015), page 117: the reader should note that monosyllabic lengthening did not occur in PGmc. *hʷát "what" (< PIE *kʷód; not PGmc. ˟hʷṓt) or *át "at" (< PIE *ád; not PGmc.˟ṓt), two words of similar shape (Ringe 2006:98).
