A telescoping method for double summations

We present a method to prove hypergeometric double summation identities. Given a hypergeometric term F ( n , i , j ) , we aim to find a difference operator L = a 0 ( n ) N 0 + a 1 ( n ) N 1 + ⋯ + a r ( n ) N r and rational functions R 1 ( n , i , j ) , R 2 ( n , i , j ) such that LF = Δ i ( R 1 F ) + Δ j ( R 2 F ) . Based on simple divisibility considerations, we show that the denominators of R 1 and R 2 must possess certain factors which can be computed from F ( n , i , j ) . Using these factors as estimates, we may find the numerators of R 1 and R 2 by guessing the upper bounds of the degrees and solving systems of linear equations. Our method is valid for the Andrews–Paule identity, Carlitzʹs identities, the Apéry–Schmidt–Strehl identity, the Graham–Knuth–Patashnik identity, and the Petkovšek–Wilf–Zeilberger identity.