Originally Posted by

**emakarov** There is a question whether the last part reads (a ring of) (sets that contain U), as the grammar suggest, or (a ring of sets) (which contain U). Since U is the universal set, I don't see much sense in talking about sets that contain U. So, I think, the last part should read "a ring of sets which contain*s* U".

I think you need the other direction. "A Boolean algebra of sets can be described as a ring of sets" to me means that every Boolean algebra (1) is a ring of sets and (2) contains U.