ϕ23⁡(a,b,ca⁢q/b,a⁢q/c;q,a⁢q⁢zb⁢c)=(a⁢z;q)∞(z;q)∞⁢ϕ45⁡(a12,-a12,(a⁢q)12,-(a⁢q)12,a⁢q/(b⁢c)a⁢q/b,a⁢q/c,a⁢z,q/z;q,q).