\[\left(1-\frac{a}{q}\right)\left(1-\frac{b}{q}\right)\sum_{k=0}^{n}\frac{\left(%
ap^{k},bp^{-k};q\right)_{n-1}(1-(ap^{2k}/b))}{\left(p;p\right)_{n}\left(p;p%
\right)_{n-k}\left(ap^{k}/b;q\right)_{n+1}}(-1)^{k}p^{\genfrac{(}{)}{0.0pt}{}{%
k}{2}}=\delta_{n,0}.\]