F⁡(a,bc;z)⁢F⁡(a,bc;ζ)=∑s=0∞(a)s⁢(b)s⁢(c-a)s⁢(c-b)s(c)s⁢(c)2⁢s⁢s!⁢(z⁢ζ)s⁢F⁡(a+s,b+sc+2⁢s;z+ζ-z⁢ζ),