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\begin{document}
\begin{equation*}
  \frac{dx_1}{dt}=u,\qquad u=\text{sat}_{u_0}(k_pe+k_ix_2),\qquad \frac{dx_2}{dt}=
  \begin{cases}
    e &\text{if } |e|<e_0\\0 &\text{if } |e|\geq e_0.
  \end{cases}
\end{equation*}
\end{document}