Let $\hat{ A}_n$ be the completion by the degree of a differential operator of the $n$-th Weyl algebra with generators $x_1,\ldots,x_n,\partial^1,\ldots,\partial^n$. Consider $n$ elements $X_1,\ldots,X_n$ in $\hat{ A}_n$ of the form $$ X_i = x_i + \sum_{ K = 1}^\infty \sum_{ l = 1}^n\sum_{ j = 1}^n x_l p_{ ij}^{ K-1,l}(\partial)\partial^j, $$ where $p^{ K-1,l}_{ ij}(\partial)$ is a degree $(K-1)$ homogeneous polynomial in $\partial^1,\ldots,\partial^n$, antisymmetric in subscripts $i,j$. Then for any natural $k$ and any function $i : \{ 1,\ldots,k\}\to\{ 1,\ldots,n\}$ we prove $$ \sum_{ \sigma \in \Sigma(k)} X_{ i_{ \sigma(1)}}\cdots X_{ i_{ \sigma(k)}}\triangleright 1 = k! \,x_{ i_1}\cdots x_{ i_k}, $$ where $\Sigma(k)$ is the symmetric group on $k$ letters and $\triangleright$ denotes the Fock action of the $\hat{ A}_n$ on the space of (commutative) polynomials.
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