# Library UniMath.Bicategories.PseudoFunctors.Display.Map2Cells

The second layer of the construction of the bicategory of pseudofunctors consists of three parts. First part: we add an action of 1-cells.
Require Import UniMath.Foundations.All.
Require Import UniMath.MoreFoundations.All.
Require Import UniMath.CategoryTheory.Core.Categories.
Require Import UniMath.CategoryTheory.Core.Functors.
Require Import UniMath.CategoryTheory.PrecategoryBinProduct.
Require Import UniMath.Bicategories.Core.Bicat.
Import Bicat.Notations.
Require Import UniMath.CategoryTheory.DisplayedCats.Core.
Require Import UniMath.Bicategories.DisplayedBicats.DispBicat.
Import DispBicat.Notations.
Require Import UniMath.Bicategories.PseudoFunctors.Display.Base.
Require Import UniMath.Bicategories.PseudoFunctors.Display.Map1Cells.
Require Import UniMath.Bicategories.Core.Invertible_2cells.
Require Import UniMath.Bicategories.Core.BicategoryLaws.
Require Import UniMath.Bicategories.Core.Unitors.
Require Import UniMath.Bicategories.DisplayedBicats.Examples.DisplayedCatToBicat.
Require Import UniMath.Bicategories.DisplayedBicats.DispUnivalence.

Local Open Scope cat.

Section Map2Cells.
Variable (C D : bicat).

Definition map2cells_disp_cat_data
: disp_cat_ob_mor (map1cells C D).
Proof.
use tpair.
- exact (λ F, (X Y : C) (f g : X --> Y), f ==> g Fmor F f ==> Fmor F g).
- exact (λ F G F₂ G₂ η, (X Y : C) (f g : X --> Y) (α : f ==> g),
(ηobj η X G₂ X Y f g α) ηmor η g
=
ηmor η f (F₂ X Y f g α ηobj η Y)) ; cbn in ×.
Defined.

Definition map2cells_disp_cat_id_comp
: disp_cat_id_comp (map1cells C D) map2cells_disp_cat_data.
Proof.
split.
- intros F F₂ X Y f g α ; cbn in ×.
rewrite !vassocr.
rewrite vcomp_lunitor.
rewrite !vassocl.
rewrite rinvunitor_natural.
rewrite <- rwhisker_hcomp.
reflexivity.
- intros F G H η ε F₂ G₂ H₂ η₂ ε₂ X Y f g α ; cbn in ×.
rewrite !vassocr.
rewrite <- lwhisker_lwhisker_rassociator.
rewrite !vassocl.
apply maponpaths.
rewrite !vassocr.
rewrite lwhisker_vcomp.
rewrite ε₂.
rewrite <- lwhisker_vcomp.
rewrite !vassocl.
apply maponpaths.
rewrite !vassocr.
rewrite rwhisker_lwhisker.
rewrite !vassocl.
apply maponpaths.
rewrite !vassocr.
rewrite rwhisker_vcomp.
rewrite η₂.
rewrite <- rwhisker_vcomp.
rewrite !vassocl.
rewrite rwhisker_rwhisker_alt.
reflexivity.
Qed.

Definition map2cells_disp_cat
: disp_bicat (map1cells C D).
Proof.
use disp_cell_unit_bicat.
use tpair.
- exact map2cells_disp_cat_data.
- exact map2cells_disp_cat_id_comp.
Defined.

Definition map2cells_is_disp_univalent_2_1
: disp_univalent_2_1 map2cells_disp_cat.
Proof.
apply disp_cell_unit_bicat_univalent_2_1.
intros F G η F₂ G₂ ; simpl in ×.
repeat (apply impred ; intro).
apply D.
Defined.

Definition map2cells_is_disp_univalent_2_0
(HD_2_1 : is_univalent_2_1 D)
: disp_univalent_2_0 map2cells_disp_cat.
Proof.
use disp_cell_unit_bicat_univalent_2_0.
- apply map1cells_is_univalent_2_1.
exact HD_2_1.
- intros ; simpl.
repeat (apply impred ; intro).
apply D.
- intro ; cbn.
repeat (apply impred_isaset ; intro).
apply D.
- intros F F₂ F₂' η ; cbn in ×.
induction η as [η₁ η₂].
apply funextsec ; intro X.
apply funextsec ; intro Y.
apply funextsec ; intro f.
apply funextsec ; intro g.
apply funextsec ; intro α.
specialize (η₁ X Y f g α).
specialize (η₂ X Y f g α).
rewrite !vassocr in η₁.
rewrite vcomp_lunitor in η₁.
rewrite !vassocl in η₁.
rewrite rinvunitor_natural in η₁.
rewrite <- rwhisker_hcomp in η₁.
rewrite !vassocr in η₁.
apply rwhisker_id_inj.
use (vcomp_lcancel (lunitor _ rinvunitor _)).
{ is_iso. }
exact (!η₁).
Defined.

Definition map2cells_is_disp_univalent_2
(HD_2_1 : is_univalent_2_1 D)
: disp_univalent_2 map2cells_disp_cat.
Proof.
split.
- apply map2cells_is_disp_univalent_2_0; assumption.
- exact map2cells_is_disp_univalent_2_1.
Defined.

End Map2Cells.