Feuerstein, Georg & Wilber, Ken: The Yoga Tradition: Its History, Literature, Philosophy and Practice, s. 104. Motilal Banarsidass Publ., 2002. ISBN 8120819233Teoksen verkkoversio.
Zilberman, David B. & Gourko, Helena & Cohen, Robert Sonné : Analogy in Indian and Western Philosophical Thought, s. 58, 91. Springer, 2006. ISBN 1402033397Teoksen verkkoversio.
