1. The problem statement, all variables and given/known data[/b] U is T1 open iff [tex]\Re[/tex]/U is countable, U=[tex]\oslash[/tex], or U=[tex]\Re[/tex]. What is the bd(0,1), the cl(rationals), and the int(rationals). 2. Relevant equations 3. The attempt at a solution Could somebody please explain this problem to me? I feel like I could try it once I understand what it is asking for. It is for my Topology class. I am confused to the fact of whether U is any set that we pick, or U is in this case bd(0,1), or Q.