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Description
This work provides a detailed description of the method for the first direct measurement of all Michel parameters in the $\tau^- \to \mu^- \bar{\nu}_\mu\nu_\tau$ decay related to the polarization of the daughter muon. An application of the suggested method in the existing and future experiments at $e^+e^-$ colliders is considered. We have performed a feasibility study for the future Super Charm-Tau Factory and Belle II experiments. For the first one, the sensitivity to the Michel parameters $\xi'$, $\xi''$, $\eta''$, $\alpha'/A$, and $\beta'/A$ is estimated. For the latter, only one Michel parameter, $\xi'$, for which the sensitivity is maximum, is considered.