this problem is from Apostol's Calculus Vol.1, i just started doing proofs so i'm still getting used to it. B - U (A) = ∩ (B-A) the U is the union of sets in a class F and ∩ is the intersection of sets in a class F. written under both the U and the ∩ are A∈F. so i let an element x ∈ B - U (A) which means that its in the set B but in none of the sets A1, A2,... in the class F. i think what i'm having trouble with is the right side of the equation. i know what it means when i have U (A) or ∩ (A) but i'm confused about ∩ (B-A). does that mean B - (A1∩A2∩A3∩...)? also is my logic correct so far?