  Letting $A \subset \mathbb{R}^n$ be Borel measurable and $W_0 : A \to
\mathbb{G}(n,m)$ Lipschitzian, we establish that \begin{equation*} \limsup_{r
\to 0^+} \frac{\mathcal{H}^m \left[ A \cap B(x,r) \cap (x+
W_0(x))\right]}{\alpha(m)r^m} \geq \frac{1}{2^n}, \end{equation*} for
$\mathcal{L}^n$-almost every $x \in A$. In particular, it follows that $A$ is
$\mathcal{L}^n$-negligible if and only if $\mathcal{H}^m(A \cap (x+W_0(x))=0$,
for $\mathcal{L}^n$-almost every $x \in A$.
