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\begin{equation*}
  \aligned 
    \frac{dH}{dt} &= r H \left(1 - \frac{H}{k}\right) - 
      \frac{a H L}{c + H}, \qquad H \geq 0, \\
    \frac{dL}{dt} &= b \frac{a H L}{c + H} - d L, \qquad L \geq 0. \\
  \endaligned
\end{equation*}
\end{document}