G2⁡(α,α′;β,β′;x,y)=∑m,n=0∞Γ⁡(α+m)⁢Γ⁡(α′+n)⁢Γ⁡(β+n-m)⁢Γ⁡(β′+m-n)Γ⁡(α)⁢Γ⁡(α′)⁢Γ⁡(β)⁢Γ⁡(β′)⁢xm⁢ynm!⁢n!,