ŠEFČÍK, Ondřej. Notes on the function of the Indo-European velar series. In Simmelkjaer Sandgaard Hansen, Bjarne; Nielsen Whitehead, Benedicte; Olander, Thomas; Olsen, Birgit Anette.
Etymology and the European Lexicon. Wiesbaden: Reichert Verlag, 2017, p. 401-414. ISBN 978-3-95490-202-6.