^ De Vaan, Michiel (2008), “ad”, in Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill, →ISBN, page 24
↑ 3.03.1Garnier, Romain (2014), “Nouvelles réflexions sur l’effet-Kortlandt”, in Glotta[2] (in French), volume 90, Vandenhoeck & Ruprecht, pages 140-160
^ Ringe, Donald (2006), From Proto-Indo-European to Proto-Germanic (A Linguistic History of English; 1)[3], Oxford: Oxford University Press, →ISBN
^ Byrd, Andrew Miles (2015), The Indo-European Syllable (Brill's Studies in Indo-European Languages & Linguistics; 15), Leiden: Brill, page 259
^ 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, page 2258
^ Ačaṙean, Hračʻeay (1979), “ց”, in Hayerēn armatakan baṙaran [Armenian Etymological Dictionary] (in Armenian), 2nd edition, a reprint of the original 1926–1935 seven-volume edition, volume IV, Yerevan: University Press, page 446a
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).
