On a hypergeometric identity of Gelfand, Graev and Retakh
arXiv:math/0303061
Abstract
A hypergeometric identity equating a triple sum to a single sum, originally found by Gelfand, Graev and Retakh [Russian Math. Surveys 47 (1992), 1-88] by using systems of differential equations, is given hypergeometric proofs. As a bonus, several -analogues can be derived.
considerably revised and extended; more -analogues are derived; in particular, a new section has been added with -analogues which are not only valid formally but also analytically