\[
\boxed{
\phi \left( f \left( x,y \left( x \right) ,{\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) ,g \left( x,y \left( x \right) ,{\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right)  \right) =0}
\]