$\Re\left(\Phi^{(\mathrm{U})}\left(s_{j}(\mathbf{x}),t_{j}(\mathbf{x});\mathbf{%
x}\right)-\Phi^{(\mathrm{U})}\left(s_{\mu}(\mathbf{x}),t_{\mu}(\mathbf{x});%
\mathbf{x}\right)\right)=0,$