Suppose there exists a Lebesgue Space, $L_1$ and functions functions $\phi$, $\phi'$, $f$, and $f'$ functions where $$\phi, \phi' \in L_1$$
By rule of integration by parts, $$uv|_a^b = \int_a^b udv + \int_a^b vdu$$
Let $$ u = \phi, du= \phi'$$ $$ v = f, dv = f'$$
Are there any properties of Lebesgue functions that allow
$$ uv|_a^b = 0$$
Are $\phi$ and $\phi'$ convergent as integrals? Do the unbounded limits of $\phi$ and $\phi'$ converge?
By the definition of Lebesgue spaces,
If $\phi \in L_1$ then $\int_{-\infty}^{\infty} \phi(x)\, dx < \infty$
If $\lim_{x \to \infty} \phi(x) > 0$ or $\lim_{x \to \infty} \phi(x) < 0$ then $\int_{-\infty}^\infty |\phi(x)| dx = \infty$
The contrapositive of the preceding statement is $ \int_{-\infty}^\infty | \phi(x) | dx \ne \infty$ then $\lim_{x \to \infty} \phi(x) = 0$
Integration by parts is usually applied as $a = -\infty$ and $b = \infty$ $uv|_{\infty}^{\infty}$ will evaluate to 0 because the unbounded integral of $\phi(x)$ converges.