Isomorphism to Closed Interval

Theorem
Let $m, n \in \N$ such that $m < n$.

Then:
 * $\left|{\left[{m + 1 \,.\,.\, n}\right]}\right| = n - m$

Let $h: \N_{n - m} \to \left[{m + 1 \,.\,.\, n}\right]$ be the mapping defined as:


 * $\forall x \in \N_{n - m}: h \left({x}\right) = x + m + 1$

Then $h$ is the unique isomorphism as defined in Unique Isomorphism between Finite Totally Ordered Sets, where the orderings on $\left[{m + 1 \,.\,.\, n}\right]$ and $\N_{n - m}$ are those induced by the ordering of $\N$.