F4⁡(α;β;γ,γ′;x⁢(1-y),y⁢(1-x))=Γ⁡(γ)⁢Γ⁡(γ′)Γ⁡(α)⁢Γ⁡(β)⁢Γ⁡(γ-α)⁢Γ⁡(γ′-β)⁢∫01∫01uα-1⁢vβ-1⁢(1-u)γ-α-1⁢(1-v)γ′-β-1(1-u⁢x)γ+γ′-α-1⁢(1-v⁢y)γ+γ′-β-1⁢(1-u⁢x-v⁢y)α+β-γ-γ′+1⁢ⅆ⁡u⁢ⅆ⁡v,