\[
\boxed{
 \left\{ {\frac {\rm d}{{\rm d}t}}x \left( t \right) =h \left( a-x \left( t \right)  \right)  \left( c-x \left( t \right) -y \left( t \right)  \right) ,{\frac {\rm d}{{\rm d}t}}y \left( t \right) =k \left( b-y \left( t \right)  \right)  \left( c-x \left( t \right) -y \left( t \right)  \right)  \right\} }
\]