 Assuming FA, the fixed points are unique; frequently they are the  empty set.    With AFA, the greatest fixed points usually have non-wellfounded  members.    We shall study this in more detail when we turn to coalgebra. For now,  we return to the last of the example equations at the top of this section,  V   =  ℘V.  This equation has no solutions in sets due to  Cantor’s Theorem. However, in terms of classes, this equation does have solutions, as we know.   The universal class  V  is a solution, as we have seen.    And the class WF of well-founded sets is a solution.   This is the  smallest solution ℘*, and   V  is the largest.    Under FA,  ℘*  = V    = ℘*.   Under AFA,   ℘*   and ℘* are different:  ℘*  = WF, and  ℘* =  V  and thus contains  sets such as  Ω= {Ω}. 