Let $a \in S^0(T^*\mathbb{R}^n)$ be a real-valued semiclassical symbol satisfying
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\begin{align*}
a(x,\xi) \geq 0
\end{align*}
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for every $(x,\xi) \in T^*\mathbb{R}^n \cong \mathbb{R}^n \times \mathbb{R}^n$. Then there exist an integer $N \in \mathbb{N}$ and constants $C > 0$ and $h_0 > 0$, depending only on $n$ and on the finitely many symbol seminorms