Section NatTrans_Props.
Context {C C' : Category}.

(** The composition of natural transformations is associative. *)
Theorem NatTrans_compose_assoc {F G H I : (C –≻ C')%functor} (N : F –≻ G)
(N' : G –≻ H) (N'' : H –≻ I)
: ((N'' ∘ N') ∘ N = N'' ∘ (N' ∘ N))%nattrans
.