The simplest case of the problem I'm thinking about involves an elliptic differential operator, $Lu = -u'' + qu$, on the interval $(0,1)$, with homogeneous Dirichlet boundary conditions. I want to show that the bilinear form on $H\_0^1 \subset H\_1$ defined by


$a(u,v) = \int\_0^1 u'v' + quv~dx$


is bounded for the $H^1$-norm, i.e., $|a(u,v)| \leq M\|u\|\_1\|v\|\_1$ for some constant $M>0$.


My question: can I assume that the linear coefficient $q$ is $L^1$ or even $L^2$ and still guarantee boundedness?


I was thinking that this is possible, but the only books that I have lying around discussing this consider only the case when $q$ is smooth or $L^\infty$. I've played around with the Cauchy-Schwarz inequality for the term $\int quv$ but am not getting anywhere.



variational formulation: boundedness of the bilinear form
Of course, as Helge says, the $H^1(0,1)$ norm controls the $L^\infty(0,1)$ norm, so you just write 
$$ \left| \int quv \right| \le \|q\|\_{L^1} \|u\| \_{L^\infty} \|v\| \_{L^\infty} \le C 
\|q\| \_{L^1} \|u\| \_{H^1} \|v\| \_{H^1}.$$


