[http://www.kortlandt.nl/publications/art208e.pdf]* Frederik Kortlandt, "From Proto-Indo-European to Slavic"* Gilbert C. Rappaport, "A Minimalist Approach to Case Marking in Slavic"* Alan Timberlake, 1978, "On the History of the Velar Phonemes in North Slavic" Russian with English synopsis.
[http://www.kortlandt.nl/publications/art208e.pdf]* Frederik Kortlandt, "From Proto-Indo-European to Slavic"* Gilbert C. Rappaport, "«A Minimalist Approach to Case Marking in Slavic»"* Alan Timberlake, 1978, «On the History of the Velar Phonemes in North Slavic» Russian with English synopsis.