Abel, N. H. "Beweis eines Ausdrucks, von welchem die Binomial-Formel ein einzelner Fall ist." J. reine angew. Math.1,
159-160, 1826. Reprinted in Œuvres Complètes, 2nd ed., Vol. 1.
pp. 102-103, 1881.Bhatnagar, G. "Inverse Relations, Generalized
Bibasic Series, and Their Extensions." PhD thesis. Columbus, OH: Ohio State
University, p. 51, 1995.Riordan, J. Combinatorial
Identities. New York: Wiley, p. 18, 1979.