End natiso_def.
Section about_isIso.
Variables (A B : Category) (F G : Functor A B) (T : NT F G).
(* qq a. Ta isIso => T isIso *)
Variable h : forall a : A, G a --> F a.
Hypothesis H : forall a : A, AreIsos (T a) (h a).

Lemma NTinv_nt_law : NT_law h.
Canonical Structure NTinv := Build_NT NTinv_nt_law.