by Herb Wilf and Doron Zeilberger.
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Appeared in J. Amer. Math. Soc. 3(1990), 147-158.
This is the Steele-prize-winning WZ classic.
Added Feb. 6, 2017: Bryan Ek found a minor typo:
p. 9, Example 3', F'(n,k) should be multiplied by -1.
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