\[
\boxed{
{\it d4y} \left( x \right) +a \left( bx-1 \right) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) +ab{\frac {\rm d}{{\rm d}x}}y \left( x \right) +\lambda\,y \left( x \right) =0}
\]