reserve X for set;
reserve UN for Universe;

theorem Th44:
  for X being set holds Tarski-Class {} c= Tarski-Class X
  proof
    let X be set;
    set T1 = Tarski-Class {},
        T2 = Tarski-Class X;
A1: T1 is_Tarski-Class_of {} & for D be set st D is_Tarski-Class_of {}
    holds T1 c= D by CLASSES1:def 4;
    {} c= T2 & T2 is Tarski & not T2,{} are_equipotent by CARD_1:26;
    then {} in T2;
    hence thesis by A1,CLASSES1:def 3;
  end;
