Restriction of Well-Ordering is Well-Ordering

Theorem
Let $S$ be a set or class.

Let $\preceq$ be a well-ordering of $S$.

Let $T$ be a subset or subclass of $S$.

Let $\preceq'$ be the restriction of $\preceq$ to $T$.

Then $\preceq'$ well-orders $T$.

Proof
By the definition of well-ordering, $\preceq$ is a well-founded total ordering.

By Totally Ordered Subset, $\preceq'$ is a total ordering.

By Restriction of Well-Founded Ordering, $\preceq'$ is well-founded.

Thus $\preceq'$ is a well-ordering.