theorem Th24:
  Y in Tarski-Class X implies card Y in card Tarski-Class X
proof
  assume
A1: Y in Tarski-Class X;
 bool Y c= Tarski-Class X
  by A1,Th3;
  then  card
 Y in card bool Y & card bool Y c= card Tarski-Class X by CARD_1:11,14;
  hence thesis;
end;
