Delta exponential with t=s

Theorem

Let $\mathbb{T}$ be a time scale, let $t \in \mathbb{T}$, and $p \colon \mathbb{T} \rightarrow \mathbb{C}$ a regressive function. The following formula holds: $$e_p(t,t;\mathbb{T})=1,$$ where $e_p$ denotes the delta exponential.