I've learned that a second order equation is transformable into SL using the integrating factor $F(x)=\exp\int^{x}{\frac{r(u)-p'(u)}{p(u)}du}$.
But are all second order diff eq's transformable or are there exceptions?
For example, if a second order doesn't have a weight ($\rho(x) = 0$) can it still be transformed into SL?