(** * Product Category *)
Require Import Basics.Tactics.
[Loading ML file number_string_notation_plugin.cmxs (using legacy method) ... done]
Require Import Category.Strict.
Require Import Types.Prod.

Set Universe Polymorphism.
Set Implicit Arguments.
Generalizable All Variables.
Set Asymmetric Patterns.

Local Open Scope category_scope.
Local Open Scope morphism_scope.

(** ** Definition of [*] for categories *)
Section prod.
  Variables C D : PreCategory.

  Definition prod : PreCategory.
C, D: PreCategory
PreCategory
    refine (@Build_PreCategory
              (C * D)%type
              (fun s d => (morphism C (fst s) (fst d)
                           * morphism D (snd s) (snd d))%type)
              (fun x => (identity (fst x), identity (snd x)))
              (fun s d d' m2 m1 => (fst m2 o fst m1, snd m2 o snd m1))
              _
              _
              _
              _);
    abstract (
        repeat (simpl || intros [] || intro);
        try f_ap; auto with morphism
      ).
  Defined.
End prod.

Local Infix "*" := prod : category_scope.

(** ** The product of strict categories is strict *)
Global Instance isstrict_category_product
       `{IsStrictCategory C, IsStrictCategory D}
: IsStrictCategory (C * D).
C: PreCategory
IsStrictCategory0: IsStrictCategory C
D: PreCategory
IsStrictCategory1: IsStrictCategory D
IsStrictCategory (C * D)
Proof.
C: PreCategory
IsStrictCategory0: IsStrictCategory C
D: PreCategory
IsStrictCategory1: IsStrictCategory D
IsStrictCategory (C * D)
  typeclasses eauto.
Qed.

Module Export CategoryProdNotations.
  Infix "*" := prod : category_scope.
End CategoryProdNotations.