Let $n,m\in\mathbb{N}$. Let $U\subseteq \mathbb{R}^n$ be \reftext{def:open-subset-euclidean-space-2026a}{open}, and let $f:U\to\mathbb{R}^m$ be a \reftext{def:c1-map-euclidean-open-set-2026a}{$C^1$ map}. Then for every point $a\in U$, the map $f$ is \reftext{def:differentiable-map-at-point-euclidean-2026a}{differentiable} at $a$.