[SOLVED] open sets in R^2 1. The problem statement, all variables and given/known data If A, B are open in R^2, and A is contained in the closure(B), then is it true that A is contained in B? 2. Relevant equations 3. The attempt at a solution It seems intuitively true. If a is in A, then there is a sequence b_n in B that converges to a by definition of closure. But I don't know what to do with that?