(** * Definition of a univalent/saturated precategory, or just "category" *)
Require Import Category.Core Category.Morphisms.
[Loading ML file number_string_notation_plugin.cmxs (using legacy method) ... done]
Require Import HoTT.Basics HoTT.Tactics.

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

Local Open Scope morphism_scope.

(** A category is a precategory for which [idtoiso] is an equivalence. *)

Notation IsCategory C := (forall s d : object C, IsEquiv (@idtoiso C s d)).

Notation isotoid C s d := (@equiv_inv _ _ (@idtoiso C s d) _).

(** *** The objects of a category are a 1-type *)

Instance trunc_category `{IsCategory C} : IsTrunc 1 C | 10000.
C: PreCategory
IsCategory0: IsCategory C
IsTrunc 1 C
Proof.
C: PreCategory
IsCategory0: IsCategory C
IsTrunc 1 C
  apply istrunc_S.
C: PreCategory
IsCategory0: IsCategory C
forall x y : C, IsHSet (x = y)
  intros ? ?.
C: PreCategory
IsCategory0: IsCategory C
x, y: C
IsHSet (x = y)
  eapply istrunc_equiv_istrunc;
  [ symmetry;
    esplit;
    apply_hyp
  | ].
C: PreCategory
IsCategory0: IsCategory C
x, y: C
IsHSet (x <~=~> y)%category
  typeclasses eauto.
Qed.

Record Category :=
  {
    precategory_of_category :> PreCategory;
    iscategory_precategory_of_category :> IsCategory precategory_of_category
  }.

Existing Instance iscategory_precategory_of_category.