Pre-differentiable

Let $\mathbb{T}$ be a time scale and let $f \colon \mathbb{T} \rightarrow \mathbb{R}$. We say that $f$ is pre-differentiable with region of differentiation $D \subset \mathbb{T}^{\kappa}$ if $f$ id delta differentiable at all $t \in D$ and $\mathbb{T}^{\kappa} \setminus D$ is countable and contains no right-scattered points in $\mathbb{T}$.