theorem Th34:
  for S being stack of X/== ex s st S = Class(==_X, s)
  proof
    let S be stack of X/==;
    the carrier' of X/== = Class(==_X)by Def20; then
    S in Class(==_X); then
    ex x being object
      st x in the carrier' of X & S = Class(==_X,x) by EQREL_1:def 3;
    hence thesis;
  end;
