Cardinality of Integer Interval

Theorem
Let $a,b\in\Z$ be integers.

Let $\left[{a \,.\,.\, b}\right]$ denote the integer interval between $a$ and $b$.

Then $\left[{a \,.\,.\, b}\right]$ is finite and its cardinality equals:
 * $\begin{cases}b-a+1 & : b \geq a-1 \\ 0 & : b \leq a-2\end{cases}$

Proof
Use Translation of Integer Interval is Bijection