Does anyone know of some good references for a fractional Leibniz rule for pseudodifferential operators of negative order? As a specific example, I would like to compute $\partial_{x}^{1}(uv)$, assuming $\xi \neq 0$ in phase space and meanzero $u,v$.
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Let $P$ be a pseudodifferential operator with symbol $p(x,\xi)$ belonging to $S^m_{1,0}$ and let $a(x)$ be a $C^\infty$ function. Then the operator $Pa$ defined by $Pa u=P(au)$ is a pseudodifferential operator of order $m$ with symbol $q(x,\xi)$ such that $$ q\sum_{\vert \alpha\vert\le N} \frac{1}{i^{\vert \alpha\vert}\alpha !}(\partial_\xi^\alpha p)(x,\xi) (\partial_x^\alpha a)(x)\in S^{mN1}_{1,0}, $$ which provides an asymptotic expansion of the symbol of the operator Pa, following simply from the composition formula. 

