A discrete Function is called closed form (or sometimes ``hypergeometric'') in two variables if the
ratios
and
are both Rational Functions. A pair of
closed form functions is said to be a Wilf-Zeilberger Pair if

**References**

Petkovsek, M.; Wilf, H. S.; and Zeilberger, D. *A=B.* Wellesley, MA: A. K. Peters, p. 141, 1996.

Zeilberger, D. ``Closed Form (Pun Intended!).'' *Contemporary Math.* **143**, 579-607, 1993.

© 1996-9

1999-05-26