reserve fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  X,Y for set,
  x,y for object;

theorem Th5:
  union On X is epsilon-transitive epsilon-connected set
proof
  x in On X implies x is Ordinal by ORDINAL1:def 9;
  hence thesis by ORDINAL1:23;
end;
