Timings for iso.v

Require Import HoTT.Basics.

Require Import Types.Universe.

Require Import HSet.

Require Import HIT.epi HIT.unique_choice.

Local Open Scope path_scope.

(** We prove that [epi + mono <-> IsEquiv] *)

Section iso.

  Context `{Univalence}.

  Variables X Y : HSet.

  Variable f : X -> Y.

  Lemma atmost1P_isinj (injf : IsInjective f)
  : forall y : Y, atmost1P (fun x => f x = y).

  Proof.

    intros y x x' p q.

    apply (injective f).

    exact (p @ q^).

  Defined.

  Definition isequiv_isepi_ismono (epif : isepi f) (monof : ismono f)
  : IsEquiv f.

  Proof.

    pose proof (@isepi_issurj _ _ _ f epif) as surjf.

    pose proof (isinj_ismono _ monof) as injf.

    pose proof (unique_choice
                  (fun y x => f x = y)
                  _
                  (fun y => (@center _ (surjf y), atmost1P_isinj injf y)))
      as H_unique_choice.

    apply (isequiv_adjointify _ H_unique_choice.1).

    -

 intro.

      apply H_unique_choice.2.

    -

 intro.

      apply injf.

      apply H_unique_choice.2.

  Defined.

End iso.