PI Artin--Schelter regular algebras of dimension 3 are unique factorization rings

We prove that all noetherian PI Artin–Schelter regular algebras of dimension $3$ are unique factorization rings. In a certain sense, this result is a noncommutative analogue to the fact that regular local rings of dimension 3 are UFDs. The fact constitutes a crucial component in the proof of the assertion that all regular local rings are UFDs, known as the Auslander–Buchsbaum theorem.