Let $X = (x_1,x_2,\dots)$ and $Y = (y_1,y_2,\dots)$ be two independent alphabets, and let $\operatorname{Sym}_{\mathbb{Q}}[X]$ and $\operatorname{Sym}_{\mathbb{Q}}[Y]$ denote the rings of symmetric functions over $\mathbb{Q}$ in the alphabets $X$ and $Y$, respectively. Let $\langle \cdot,\cdot\rangle_X$ be the Hall [inner product](/page/Inner%20Product) in the $X$ variables, characterized by
\begin{align*}
\langle s_\lambda[X],s_\mu[X]\rangle_X=\delta_{\lambda\mu}
\end{align*}
for all integer partitions $\lambda$ and $\mu$. If the Cauchy kernel is
\begin{align*}
\Omega[X,Y]=\sum_{\lambda}s_\lambda[X]s_\lambda[Y],
\end{align*}
where the sum ranges over all integer partitions $\lambda$, then for every $f \in \operatorname{Sym}_{\mathbb{Q}}$,
\begin{align*}
\langle f[X],\Omega[X,Y]\rangle_X=f[Y].
\end{align*}…