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

theorem :: Theorem 2 (4)
  X c= Rrank Y implies Rrank X c= Rrank Y
proof
  assume X c= Rrank Y;
  then the_rank_of X c= the_rank_of Y by CLASSES1:65;
  hence thesis by CLASSES1:37;
end;
