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

theorem
  for X be epsilon-transitive set holds
    Tarski-Class X = GrothendieckUniverse X
proof
  let X be epsilon-transitive set;
  Tarski-Class X is Grothendieck of X by Def4,CLASSES1:2;
  hence thesis by GDef,Th18;
end;
