reserve W,X,Y,Z for set,
  f,g for Function,
  a,x,y,z for set;

theorem
  Y c= Tarski-Class X & card Y in card Tarski-Class X implies
  Y in Tarski-Class X
proof
  assume that
A1: Y c= Tarski-Class X and
A2: card Y in card Tarski-Class X;
 card Y <> card Tarski-Class X by A2;
  hence thesis by A1,Th5,CARD_1:5;
end;
