theorem
  E is epsilon-transitive implies (E |= the_axiom_of_unions iff for X st
  X in E holds union X in E)
proof
  assume
A1: E is epsilon-transitive;
  hence E |= the_axiom_of_unions implies for X st X in E holds union X in E by
Th4;
  assume for X st X in E holds union X in E;
  then for u holds union u in E;
  hence thesis by A1,Th4;
end;
