The hierarchy of omega1-Borel sets
  The family omega1-Borel sets is the smallest family of subsets of the real line which contains the family of open sets and is closed under complementation and omega1 unions. We show:   Theorem 1. MA+notCH implies this hierarchy has length omega2.   Theorem 2. In the Cohen real model it has length either omega1+1 or omega1+2. 
Arnold W. Miller
math.LO