Let $n \in \mathbb{N}$, let $s \in \mathbb{R}$, and let $h > 0$. Let $\mathcal{L}^n$ denote $n$-dimensional Lebesgue measure on $\mathbb{R}^n$, and let $L^2(\mathbb{R}^n)$ mean $L^2(\mathbb{R}^n, \mathcal{B}(\mathbb{R}^n), \mathcal{L}^n)$. For $\xi \in \mathbb{R}^n$, write