ϕ12⁡(a,bc;q,z)=(a⁢b⁢z/c,q/c;q)∞(a⁢z/c,q/a;q)∞⁢ϕ12⁡(c/a,c⁢q/(a⁢b⁢z)c⁢q/(a⁢z);q,b⁢q/c)-(b,q/c,c/a,a⁢z/q,q2/(a⁢z);q)∞(c/q,b⁢q/c,q/a,a⁢z/c,c⁢q/(a⁢z);q)∞⁢ϕ12⁡(a⁢q/c,b⁢q/cq2/c;q,z),