ⅆ2⁡wⅆ⁡z2=12⁢(1w+1w-1+1w-z)⁢(ⅆ⁡wⅆ⁡z)2-(1z+1z-1+1w-z)⁢ⅆ⁡wⅆ⁡z+w⁡(w-1)⁢(w-z)z2⁢(z-1)2⁢(α+β⁢zw2+γ⁢(z-1)(w-1)2+δ⁢z⁢(z-1)(w-z)2),