A note on $UFD$

We search for principal ideals. As a sample, let $R$ be a strongly-normal, almost-factorial, and complete-intersection local ring with a prime ideal $P$ of height one. If $depth(R/ P)\geq dim R-2$, we show $P$ is principal. As an immediate corollary, we apply some easy local cohomology arguments and reprove a celebrated theorem of Auslander-Buchsbaum, simplifying a result of Dao and Samuel. From this, we show the hypersurface property of rings of multiplicity at most three. As another application, we answer affirmatively a question posted by Braun.