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;
reserve m,n for Nat;
reserve x1,x2,x3,x4,x5,x6,x7,x8 for object;

theorem
  for f being Function holds card rng f c= card dom f
proof
  let f be Function;
  rng f = f.:dom f by RELAT_1:113;
  hence thesis by CARD_1:66;
end;
