\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) ={\frac {y \left( x \right) }{x \left( -1+xy \left( x \right) +x \left( y \left( x \right)  \right) ^{3}+x \left( y \left( x \right)  \right) ^{4} \right) }}=0}
\]