Definition:Piecewise Continuously Differentiable Function/Definition 1

Definition
Let $f$ be a real function defined on a closed interval $\left[{a \,.\,.\, b}\right]$.

$f$ is piecewise continuously differentiable iff:


 * $(1): \quad$ $f$ is continuous
 * $(2): \quad$ there exists a finite subdivision $\left\{{x_0, \ldots, x_n}\right\}$ of $\left[{a \,.\,.\, b}\right]$, $x_0 = a$ and $x_n = b$, such that $f$ is continuously differentiable on $\left({x_{i−1} \,.\,.\, x_i}\right)$ and the one-sided limits $\displaystyle \lim_{x \to x_{i−1^+}} f′\left({x}\right)$ and $\displaystyle \lim_{x \to x_{i^-}} f′\left({x}\right)$ exist for every $i \in \left\{{1, \ldots, n}\right\}$.

Note that $f′$ is piecewise continuous.