\[\lim_{\tau\to 0}\frac{\left(a/\tau;q\right)_{n}\left(b/\tau;q\right)_{n}}{%
\left(c/\tau^{2};q\right)_{n}}=(-1)^{n}\left(\frac{ab}{c}\right)^{n}q^{%
\genfrac{(}{)}{0.0pt}{}{n}{2}}.\]