\[b(1-a){{}_{2}\phi_{1}}\left({aq,b\atop c};q,z\right)-a(1-b){{}_{2}\phi_{1}}%
\left({a,bq\atop c};q,z\right)=(b-a){{}_{2}\phi_{1}}\left({a,b\atop c};q,z%
\right),\]