reserve A,B for Ordinal,
  K,M,N for Cardinal,
  x,x1,x2,y,y1,y2,z,u for object,X,Y,Z,X1,X2, Y1,Y2 for set,
  f,g for Function;

theorem Th20:
  K*`1 = K
proof
  K = card K;
  hence thesis by CARD_1:69,ORDINAL3:15;
end;
