Equicontinuity + pointwise boundedness implies uniform boundedness on compact sets
On a compact domain, equicontinuity upgrades pointwise bounds to a global bound
Let be a compact metric space and let be a family of continuous functions. Assume:
- is equicontinuous on , and
- is pointwise bounded on (for each , ).
Lemma: Then is uniformly bounded on ; i.e., there exists such that
Remarks
This lemma is a standard step in the proof of the Arzelà–Ascoli theorem.