Helimski, Eugene. Proto-Uralic gradation: Continuation and traces
– In: Congressus Octavus Internationalis Fenno-Ugristarum. Pars I: Orationes plenariae et conspectus quinquennales. Jyväskylä, 1995. "Archived copy"(PDF). Archived from the original(PDF) on 2 October 2011. Retrieved 24 February 2012.{{cite web}}: CS1 maint: archived copy as title (link)
Helimski, Eugene. Proto-Uralic gradation: Continuation and traces
– In: Congressus Octavus Internationalis Fenno-Ugristarum. Pars I: Orationes plenariae et conspectus quinquennales. Jyväskylä, 1995. "Archived copy"(PDF). Archived from the original(PDF) on 2 October 2011. Retrieved 24 February 2012.{{cite web}}: CS1 maint: archived copy as title (link)
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Petri, Kallio (2012), "The non-initial-syllable vowel reductions from Proto-Uralic to Proto-Finnic", Suomalais-Ugrilaisen Seuran Toimituksia, 264, ISSN0355-0230
Ravila, Paavo (1929), "Über eine doppelte vertretung des urfinnischwolgaischen *a der nichtersten silbe im mordwinischen", Finnisch-Ugrische Forschungen, 20, ISSN0355-1253