reserve m for Cardinal,
  A,B,C for Ordinal,
  x,y,z,X,Y,Z,W for set,
  f for Function;

theorem Th11:
  W is Tarski & X in W implies card X in W
proof
  assume that
A1: W is Tarski and
A2: X in W;
A3: card W = On W by A1,Th9;
  card X in card W by A1,A2,Th1;
  hence thesis by A3,ORDINAL1:def 9;
end;
