F2⁡(α;β,β′;γ,γ′;x,y)=Γ⁡(γ)⁢Γ⁡(γ′)Γ⁡(β)⁢Γ⁡(β′)⁢Γ⁡(γ-β)⁢Γ⁡(γ′-β′)⁢∫01∫01uβ-1⁢vβ′-1⁢(1-u)γ-β-1⁢(1-v)γ′-β′-1(1-u⁢x-v⁢y)α⁢ⅆ⁡u⁢ⅆ⁡v,