Let $f,g: R \rightarrow R$ be two positive increasing functions. Under what (non-trivial) conditions one can guarantee that $\int\_{0}^{\infty}f'g dx\geq \int\_{0}^{\infty}g'fdx$. 



An elementary question about integration by parts!
Say, if $f/g$ is nondecreasing (plus something to take care of convergence), but that's way too strong.


