 As we have seen, one formulation of FA says that every set belongs to some Vα.  This is a mathematical formulation of the iterative concept of set: sets are just what one gets by iterating the power set operation on the well-ordered class of ordinal numbers.  We start with nothing, the empty set.[7] This is V0.  Then we form  V1 =  ℘V0.   Then  V2 =  ℘V1. Going on, when we come to the first limit ordinal ω, we take  Vω to be  the union of all the sets Vn.     Then we proceed to Vω+ 1  = ℘ Vω.   We continue like this absolutely forever, going through “all the ordinal numbers”.  The collection so described is the universe V of sets. 