reserve W,X,Y,Z for set,
  f,g for Function,
  a,x,y,z for set;
reserve u,v for Element of Tarski-Class(X),
  A,B,C for Ordinal,
  L for Sequence;

theorem Th25:
  Y in Tarski-Class X implies not Y,Tarski-Class X are_equipotent
proof
  assume Y in Tarski-Class X;
then  card Y in card Tarski-Class X by Th24;
then  card Y <> card Tarski-Class X;
  hence thesis by CARD_1:5;
end;
