θ⁡(x+y+u+v2|Ω)⁢θ⁡(x+y-u-v2|Ω)⁢θ⁡(x-y+u-v2|Ω)⁢θ⁡(x-y-u+v2|Ω)=12g⁢∑α∈12⁢ℤg/ℤg∑β∈12⁢ℤg/ℤgⅇ2⁢π⁢ⅈ⁢(2⁢α⋅Ω⋅α+α⋅[x+y+u+v])⁢θ⁡(x+Ω⁢α+β|Ω)⁢θ⁡(y+Ω⁢α+β|Ω)⁢θ⁡(u+Ω⁢α+β|Ω)⁢θ⁡(v+Ω⁢α+β|Ω),