Exercise 7, § 2

Let $\mathbf{f}$ be a continuous vector function defined on an open interval $I \subset \mathbf{R}$, with values in a normed space $E$ over $\mathbf{R}$, and admitting a right derivative at every point of $I$. Show that the set of points of $I$ where $\mathbf{f}$ admits a derivative is the complement of a meagre subset of $I$ (use exerc. 5 b) of I, p. 36, and prop. 6 of I, p. 18).