Exact results on $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}+2\mathrm{}\gamma$ in the $Z^0$-resonance region

We use the methods of the CALKUL Collaboration to calculate the differential cross section for $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}+2\mathrm{}\gamma$ near the $Z^0$ resonance. An explicit complete formula for the cross section is obtained. The formula is checked against a leading-log approximation and against one obtained by spinor techniques. Applications to high-precision $Z^0$ physics are discussed.