Let $f : \mathbb{R}^N \to \mathbb{R}$ be a D4364: Real function such that

(i)	\begin{equation} \exists \, C \in \mathbb{R} : \forall \, x \in \mathbb{R}^N : f(x) = C \end{equation}

Let $L : \mathbb{R}^N \to \mathbb{R}$ be a D4364: Real function such that

(i)	\begin{equation} \forall \, x \in \mathbb{R}^N : L(x) = 0 \end{equation}

Then $L$ is a D5681: Real function derivative for $f$ on $\mathbb{R}^N$.