Let $U\subsetneq\mathbb R^n$ be bounded and open. Suppose $a_{ij},b_i,c\in L^\infty(U)$, and let $B:H_0^1(U)\times H_0^1(U)\to\mathbb R$ be the [bilinear form](/page/Bilinear%20Form) associated to the divergence form operator
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\begin{align*}
Lu&=-\sum_{i,j=1}^n\partial_{x_i}(a_{ij}\partial_{x_j}u)+\sum_{i=1}^n b_i\partial_{x_i}u+c u.
\end{align*}