theorem
  (idt F1)" = idt F1
proof
  now
    let a be Object of A;
    thus (idt F1)"!a = ((idt F1)!a)" by Th38
      .= (idm(F1.a))" by FUNCTOR2:4
      .= idm(F1.a) by ALTCAT_3:4
      .= (idt F1)!a by FUNCTOR2:4;
  end;
  hence thesis by FUNCTOR2:3;
end;
