θ⁢[12⁢[c1+c2+c3+c4]12⁢[d1+d2+d3+d4]]⁡(x+y+u+v2|Ω)⁢θ⁢[12⁢[c1+c2-c3-c4]12⁢[d1+d2-d3-d4]]⁡(x+y-u-v2|Ω)⁢θ⁢[12⁢[c1-c2+c3-c4]12⁢[d1-d2+d3-d4]]⁡(x-y+u-v2|Ω)⁢θ⁢[12⁢[c1-c2-c3+c4]12⁢[d1-d2-d3+d4]]⁡(x-y-u+v2|Ω)=12g⁢∑α∈12⁢ℤg/ℤg∑β∈12⁢ℤg/ℤgⅇ-2⁢π⁢ⅈ⁢β⋅[c1+c2+c3+c4]⁢θ⁢[c1+αd1+β]⁡(x|Ω)⁢θ⁢[c2+αd2+β]⁡(y|Ω)⁢θ⁢[c3+αd3+β]⁡(u|Ω)⁢θ⁢[c4+αd4+β]⁡(v|Ω).