Section Hor_Compose_ids.
Context {C D E : Category} (F : (C –≻ D)%functor) (G : (D –≻ E)%functor).

Theorem NatTrans_hor_comp_ids
: ((NatTrans_id G) ∘_h (NatTrans_id F))%nattrans = NatTrans_id  (G ∘ F).