\[\mathscr{M}\mskip-3.0muf\mskip 3.0mu\left(z\right)=\mathscr{M}\mskip-3.0muf_{1%
}\mskip 3.0mu\left(z\right)+\mathscr{M}\mskip-3.0muf_{2}\mskip 3.0mu\left(z\right)\]