2. Let $u$ be an open subset of $\mathbb{R}^{2}$ and let $K$ be a compact subset of $U$. Suppuse that $f: U ightarrow \mathbb{R}$ is a function of class $\mathcal{C}^{1}(U) $ and let $E=\{(x, y) \in K \mid f(x, y)=0\}$ and that $D f$ does nut vanish on $E$. Investigate whether $E$ is a Jordun region. CS.VS. 1588||