reserve X,Y,Z for set,
        x,y,z for object,
        A,B,C for Ordinal;
reserve U for Grothendieck;

theorem :: Theorem 2 (2)
  Y in Rrank X implies ex x st x in X & Y c= Rrank x
proof
  assume Y in Rrank X;
  then ex Z st Z in X & Y in bool Rrank Z by Th4;
  hence thesis;
end;
