# Extension of PsDO to the compact operator

Let $A$ be a pseudodifferential operator of order $m < 0$, i.e. $A \in \mathcal{L}^m(\Omega)$, $\Omega \subset \mathbb{R}^n$. How to show then that A can be extened to the compact linear continuous operator from $L^2_{compact}(\Omega)$ to $L^2_{loc}(\Omega)$?

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