(**
Graphically:
#
<pre>
    C      C             C              C       
    |  N   |             |              |
  F | ===> | G           |              |
    |      |             |              |
    ∨      ∨             |   N' ∘_h N   |
    D      D        F'∘F | ===========> |G'∘G
    |  N'  |             |              |
 F' | ===> | G'          |              |
    |      |             |              |
    ∨      ∨             ∨              ∨
    E      E             E              E
</pre>
#
*)

Notation "N ∘_h N'" := (NatTrans_hor_comp N' N) : nattrans_scope.

Theorem NatTrans_id_Op : ((NatTrans_id F)^op)%nattrans = NatTrans_id (F^op)%functor.