Various families of such Special Functions as the hypergeometric functions of
one, two and more variables, and their associated summation, transformation
and reduction formulas, are potentially useful not only as solutions of
ordinary and partial differential equations, but also in the widespread
problems in the mathematical, physical, engineering and statistical
sciences. The main object of this paper is first to establish four general
double-series identities, which involve some suitably-bounded sequences of
complex numbers, by using zero-balanced terminating hypergeometric summation
theorems for the generalized hypergeometric series r+1Fr(1) (r = 1, 2, 3) in
conjunction with the series rearrangement technique. The sum (or difference)
of two general double hypergeometric functions of the Kamp? de F?riet type
are then obtained in terms of a generalized hypergeometric function under
appropriate convergence conditions. A closed form of the following Clausen
hypergeometric function: 3F2 (?27z/4(1?z)3) and a reduction formula for
the Srivastava-Daoust double hypergeometric function with the arguments
(z,?z/4 ) are also derived. Many of the reduction formulas, which are
established in this paper, are verified by using the software program,
Mathematica. Some potential directions for further researches along the
lines of this paper are also indicated.