Library UniMath.CategoryTheory.Core.TwoCategories
Require Import UniMath.Foundations.All.
Require Import UniMath.MoreFoundations.All.
Require Import UniMath.CategoryTheory.Core.Categories.
Local Open Scope cat.
Definition two_cat_data
: UU
:= ∑ (C : category)
(cells_C : ∏ (x y : C), x --> y → x --> y → UU),
(∏ (x y : C) (f : x --> y), cells_C _ _ f f)
× (∏ (x y : C) (f g h : x --> y),
cells_C _ _ f g → cells_C _ _ g h → cells_C _ _ f h)
× (∏ (x y z : C)
(f : x --> y)
(g1 g2 : y --> z),
cells_C _ _ g1 g2 → cells_C _ _ (f · g1) (f · g2))
× (∏ (x y z : C)
(f1 f2 : x --> y)
(g : y --> z),
cells_C _ _ f1 f2 → cells_C _ _ (f1 · g) (f2 · g)).
Coercion category_from_two_cat_data (C : two_cat_data)
: category
:= pr1 C.
Definition two_cat_cells
(C : two_cat_data)
{a b : C}
(f g : C⟦a, b⟧)
: UU
:= pr12 C a b f g.
Local Notation "f '==>' g" := (two_cat_cells _ f g) (at level 60).
Local Notation "f '<==' g" := (two_cat_cells _ g f) (at level 60, only parsing).
Data projections.
Definition id2 {C : two_cat_data} {a b : C} (f : C⟦a, b⟧) : f ==> f
:= pr122 C a b f.
Definition vcomp2 {C : two_cat_data} {a b : C} {f g h : C⟦a, b⟧}
: f ==> g → g ==> h → f ==> h
:= λ x y, pr1 (pr222 C) _ _ _ _ _ x y.
Definition lwhisker {C : two_cat_data} {a b c : C} (f : C⟦a, b⟧) {g1 g2 : C⟦b, c⟧}
: g1 ==> g2 → f · g1 ==> f · g2
:= λ x, pr12 (pr222 C) _ _ _ _ _ _ x.
Definition rwhisker {C : two_cat_data} {a b c : C} {f1 f2 : C⟦a, b⟧} (g : C⟦b, c⟧)
: f1 ==> f2 → f1 · g ==> f2 · g
:= λ x, pr22 (pr222 C) _ _ _ _ _ _ x.
Local Notation "x • y" := (vcomp2 x y) (at level 60).
Local Notation "f ◃ x" := (lwhisker f x) (at level 60). Local Notation "y ▹ g" := (rwhisker g y) (at level 60).
Definition hcomp {C : two_cat_data} {a b c : C} {f1 f2 : C⟦a, b⟧} {g1 g2 : C⟦b, c⟧}
: f1 ==> f2 → g1 ==> g2 → f1 · g1 ==> f2 · g2
:= λ x y, (x ▹ g1) • (f2 ◃ y).
Definition hcomp' {C : two_cat_data} {a b c : C} {f1 f2 : C⟦a, b⟧} {g1 g2 : C⟦b, c⟧}
: f1 ==> f2 → g1 ==> g2 → f1 · g1 ==> f2 · g2
:= λ x y, (f1 ◃ y) • (x ▹ g2).
Local Notation "x ⋆ y" := (hcomp x y) (at level 50, left associativity).
The numbers in the following laws refer to the list of axioms given in ncatlab
(Section "Definition / Details")
https://ncatlab.org/nlab/show/bicategorydetailedDefn
version of October 7, 2015 10:35:36
1a id2_left
1b id2_right
2 vassocr
(∏ (a b : C) (f g h k : C⟦a, b⟧) (x : f ==> g) (y : g ==> h) (z : h ==> k),
x • (y • z) = (x • y) • z)
×
x • (y • z) = (x • y) • z)
×
3a lwhisker_id2
3b id2_rwhisker
4 lwhisker_vcomp
(∏ (a b c : C) (f : C⟦a, b⟧) (g h i : C⟦b, c⟧) (x : g ==> h) (y : h ==> i),
(f ◃ x) • (f ◃ y) = f ◃ (x • y))
×
(f ◃ x) • (f ◃ y) = f ◃ (x • y))
×
5 rwhisker_vcomp
(∏ (a b c : C) (f g h : C⟦a, b⟧) (i : C⟦b, c⟧) (x : f ==> g) (y : g ==> h),
(x ▹ i) • (y ▹ i) = (x • y) ▹ i)
×
(x ▹ i) • (y ▹ i) = (x • y) ▹ i)
×
6 vcomp_whisker
(∏ (a b c : C) (f g : C⟦a, b⟧) (h i : C⟦b, c⟧) (x : f ==> g) (y : h ==> i),
(x ▹ h) • (g ◃ y) = (f ◃ y) • (x ▹ i)).
Definition two_precat : UU := ∑ C : two_cat_data, two_cat_laws C.
Coercion two_cat_data_from_two_cat (C : two_precat) : two_cat_data := pr1 C.
Coercion two_cat_laws_from_two_cat (C : two_precat) : two_cat_laws C := pr2 C.
(x ▹ h) • (g ◃ y) = (f ◃ y) • (x ▹ i)).
Definition two_precat : UU := ∑ C : two_cat_data, two_cat_laws C.
Coercion two_cat_data_from_two_cat (C : two_precat) : two_cat_data := pr1 C.
Coercion two_cat_laws_from_two_cat (C : two_precat) : two_cat_laws C := pr2 C.
Laws projections.
1a id2_left
Definition id2_left {a b : C} {f g : C⟦a, b⟧} (x : f ==> g)
: id2 f • x = x
:= pr1 (pr2 C) _ _ _ _ x.
: id2 f • x = x
:= pr1 (pr2 C) _ _ _ _ x.
1b id2_right
Definition id2_right {a b : C} {f g : C⟦a, b⟧} (x : f ==> g)
: x • id2 g = x
:= pr1 (pr2 (pr2 C)) _ _ _ _ x.
: x • id2 g = x
:= pr1 (pr2 (pr2 C)) _ _ _ _ x.
2 vassocr
Definition vassocr {a b : C} {f g h k : C⟦a, b⟧}
(x : f ==> g) (y : g ==> h) (z : h ==> k)
: x • (y • z) = (x • y) • z
:= pr1 (pr2 (pr2 (pr2 C))) _ _ _ _ _ _ x y z.
(x : f ==> g) (y : g ==> h) (z : h ==> k)
: x • (y • z) = (x • y) • z
:= pr1 (pr2 (pr2 (pr2 C))) _ _ _ _ _ _ x y z.
3a lwhisker_id2
Definition lwhisker_id2 {a b c : C} (f : C⟦a, b⟧) (g : C⟦b, c⟧)
: f ◃ id2 g = id2 _
:= pr1 (pr2 (pr2 (pr2 (pr2 C)))) _ _ _ f g.
: f ◃ id2 g = id2 _
:= pr1 (pr2 (pr2 (pr2 (pr2 C)))) _ _ _ f g.
3b id2_rwhisker
Definition id2_rwhisker {a b c : C} (f : C⟦a, b⟧) (g : C⟦b, c⟧)
: id2 f ▹ g = id2 _
:= pr1 (pr2 (pr2 (pr2 (pr2 (pr2 C))))) _ _ _ f g.
: id2 f ▹ g = id2 _
:= pr1 (pr2 (pr2 (pr2 (pr2 (pr2 C))))) _ _ _ f g.
4 lwhisker_vcomp
Definition lwhisker_vcomp {a b c : C} (f : C⟦a, b⟧) {g h i : C⟦b, c⟧}
(x : g ==> h) (y : h ==> i)
: (f ◃ x) • (f ◃ y) = f ◃ (x • y)
:= pr1 (pr2 (pr2 (pr2 (pr2 (pr2 (pr2 C)))))) _ _ _ f _ _ _ x y.
(x : g ==> h) (y : h ==> i)
: (f ◃ x) • (f ◃ y) = f ◃ (x • y)
:= pr1 (pr2 (pr2 (pr2 (pr2 (pr2 (pr2 C)))))) _ _ _ f _ _ _ x y.
5 rwhisker_vcomp
Definition rwhisker_vcomp {a b c : C} {f g h : C⟦a, b⟧}
(i : C⟦b, c⟧) (x : f ==> g) (y : g ==> h)
: (x ▹ i) • (y ▹ i) = (x • y) ▹ i
:= pr1 (pr2 (pr2 (pr2 (pr2 (pr2 (pr2 (pr2 C))))))) _ _ _ _ _ _ i x y.
(i : C⟦b, c⟧) (x : f ==> g) (y : g ==> h)
: (x ▹ i) • (y ▹ i) = (x • y) ▹ i
:= pr1 (pr2 (pr2 (pr2 (pr2 (pr2 (pr2 (pr2 C))))))) _ _ _ _ _ _ i x y.
6 vcomp_whisker