\[\theta\left(\mathbf{z}+\int_{P_{1}}^{P_{3}}\boldsymbol{{\omega}}\middle|%
\boldsymbol{{\Omega}}\right)\theta\left(\mathbf{z}+\int_{P_{2}}^{P_{4}}%
\boldsymbol{{\omega}}\middle|\boldsymbol{{\Omega}}\right)E(P_{3},P_{2})E(P_{1}%
,P_{4})+\theta\left(\mathbf{z}+\int_{P_{2}}^{P_{3}}\boldsymbol{{\omega}}%
\middle|\boldsymbol{{\Omega}}\right)\theta\left(\mathbf{z}+\int_{P_{1}}^{P_{4}%
}\boldsymbol{{\omega}}\middle|\boldsymbol{{\Omega}}\right)E(P_{3},P_{1})E(P_{4%
},P_{2})=\theta\left(\mathbf{z}\middle|\boldsymbol{{\Omega}}\right)\theta\left%
(\mathbf{z}+\int_{P_{1}}^{P_{3}}\boldsymbol{{\omega}}+\int_{P_{2}}^{P_{4}}%
\boldsymbol{{\omega}}\middle|\boldsymbol{{\Omega}}\right)E(P_{1},P_{2})E(P_{3}%
,P_{4}),\]