\[f(x)=\sum_{n=0}^{\infty}\int_{-\infty}^{\infty}\frac{{\mathrm{e}}^{-(x^{2}+y^{%
2})/2}}{{\pi}^{\frac{1}{2}}2^{n}n!}H_{n}\left(x\right)H_{n}\left(y\right)f(y)%
\,\mathrm{d}y,\]