TIFR Mathematics 2024 | Part B | Question: 10

Question

Let $f: \mathbb{R} \rightarrow \mathbb{R}$ be differentiable, and assume that $\left|f^{\prime}(x)\right| \geq 1$ for all $x \in \mathbb{R}$. Then for each compact set $C \subset \mathbb{R}$, the set $f^{-1}(C)$ is compact.