Closed Form -- from Wolfram MathWorld
https://mathworld.wolfram.com/ClosedForm.html
WEBApr 13, 2024 · A discrete function A (n,k) is called closed form (or sometimes "hypergeometric") in two variables if the ratios A (n+1,k)/A (n,k) and A (n,k+1)/A (n,k) are both rational functions. A pair of closed form functions (F,G) is said to be a Wilf-Zeilberger pair if F (n+1,k)-F (n,k)=G (n,k+1)-G (n,k).
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