lean2/hott/types/eq.hlean

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/-
Copyright (c) 2014 Floris van Doorn. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Module: types.eq
Author: Floris van Doorn
Ported from Coq HoTT
Theorems about path types (identity types)
-/
open eq sigma sigma.ops equiv is_equiv
namespace eq
/- Path spaces -/
variables {A B : Type} {a a1 a2 a3 a4 : A} {b b1 b2 : B} {f g : A → B} {h : B → A}
/- The path spaces of a path space are not, of course, determined; they are just the
higher-dimensional structure of the original space. -/
/- some lemmas about whiskering -/
definition whisker_left_con_right (p : a1 = a2) {q q' q'' : a2 = a3} (r : q = q') (s : q' = q'')
: whisker_left p (r ⬝ s) = whisker_left p r ⬝ whisker_left p s :=
begin
cases p, cases r, cases s, apply idp
end
definition whisker_right_con_right {p p' p'' : a1 = a2} (q : a2 = a3) (r : p = p') (s : p' = p'')
: whisker_right (r ⬝ s) q = whisker_right r q ⬝ whisker_right s q :=
begin
cases q, cases r, cases s, apply idp
end
definition whisker_left_con_left (p : a1 = a2) (p' : a2 = a3) {q q' : a3 = a4} (r : q = q')
: whisker_left (p ⬝ p') r = !con.assoc ⬝ whisker_left p (whisker_left p' r) ⬝ !con.assoc' :=
begin
cases p', cases p, cases r, cases q, apply idp
end
definition whisker_right_con_left {p p' : a1 = a2} (q : a2 = a3) (q' : a3 = a4) (r : p = p')
: whisker_right r (q ⬝ q') = !con.assoc' ⬝ whisker_right (whisker_right r q) q' ⬝ !con.assoc :=
begin
cases q', cases q, cases r, cases p, apply idp
end
definition whisker_left_inv_left (p : a2 = a1) {q q' : a2 = a3} (r : q = q')
: !con_inv_cancel_left⁻¹ ⬝ whisker_left p (whisker_left p⁻¹ r) ⬝ !con_inv_cancel_left = r :=
begin
cases p, cases r, cases q, apply idp
end
/- Transporting in path spaces.
There are potentially a lot of these lemmas, so we adopt a uniform naming scheme:
- `l` means the left endpoint varies
- `r` means the right endpoint varies
- `F` means application of a function to that (varying) endpoint.
-/
definition transport_eq_l (p : a1 = a2) (q : a1 = a3)
: transport (λx, x = a3) p q = p⁻¹ ⬝ q :=
by cases p; cases q; reflexivity
definition transport_eq_r (p : a2 = a3) (q : a1 = a2)
: transport (λx, a1 = x) p q = q ⬝ p :=
by cases p; cases q; reflexivity
definition transport_eq_lr (p : a1 = a2) (q : a1 = a1)
: transport (λx, x = x) p q = p⁻¹ ⬝ q ⬝ p :=
begin
cases p,
symmetry, transitivity (refl a1)⁻¹ ⬝ q,
apply con_idp,
apply idp_con
end
definition transport_eq_Fl (p : a1 = a2) (q : f a1 = b)
: transport (λx, f x = b) p q = (ap f p)⁻¹ ⬝ q :=
by cases p; cases q; apply idp
definition transport_eq_Fr (p : a1 = a2) (q : b = f a1)
: transport (λx, b = f x) p q = q ⬝ (ap f p) :=
by cases p; apply idp
definition transport_eq_FlFr (p : a1 = a2) (q : f a1 = g a1)
: transport (λx, f x = g x) p q = (ap f p)⁻¹ ⬝ q ⬝ (ap g p) :=
begin
cases p,
symmetry, transitivity (ap f (refl a1))⁻¹ ⬝ q,
apply con_idp,
apply idp_con
end
definition transport_eq_FlFr_D {B : A → Type} {f g : Πa, B a}
(p : a1 = a2) (q : f a1 = g a1)
: transport (λx, f x = g x) p q = (apd f p)⁻¹ ⬝ ap (transport B p) q ⬝ (apd g p) :=
begin
cases p,
symmetry,
transitivity _,
apply con_idp,
transitivity _,
apply idp_con,
apply ap_id
end
definition transport_eq_FFlr (p : a1 = a2) (q : h (f a1) = a1)
: transport (λx, h (f x) = x) p q = (ap h (ap f p))⁻¹ ⬝ q ⬝ p :=
begin
cases p,
symmetry,
transitivity (ap h (ap f (refl a1)))⁻¹ ⬝ q,
apply con_idp,
apply idp_con,
end
definition transport_eq_lFFr (p : a1 = a2) (q : a1 = h (f a1))
: transport (λx, x = h (f x)) p q = p⁻¹ ⬝ q ⬝ (ap h (ap f p)) :=
begin
cases p, symmetry,
transitivity (refl a1)⁻¹ ⬝ q,
apply con_idp,
apply idp_con,
end
-- The Functorial action of paths is [ap].
/- Equivalences between path spaces -/
/- [ap_closed] is in init.equiv -/
definition equiv_ap (f : A → B) [H : is_equiv f] (a1 a2 : A)
: (a1 = a2) ≃ (f a1 = f a2) :=
equiv.mk (ap f) _
/- Path operations are equivalences -/
definition is_equiv_eq_inverse (a1 a2 : A) : is_equiv (@inverse A a1 a2) :=
is_equiv.mk inverse inverse inv_inv inv_inv (λp, eq.rec_on p idp)
local attribute is_equiv_eq_inverse [instance]
definition eq_equiv_eq_symm (a1 a2 : A) : (a1 = a2) ≃ (a2 = a1) :=
equiv.mk inverse _
definition is_equiv_concat_left [instance] (p : a1 = a2) (a3 : A)
: is_equiv (concat p : a2 = a3 → a1 = a3) :=
is_equiv.mk (concat p) (concat p⁻¹)
(con_inv_cancel_left p)
(inv_con_cancel_left p)
(λq, by cases p;cases q;exact idp)
local attribute is_equiv_concat_left [instance]
definition equiv_eq_closed_left (p : a1 = a2) (a3 : A) : (a1 = a3) ≃ (a2 = a3) :=
equiv.mk (concat p⁻¹) _
definition is_equiv_concat_right [instance] (p : a2 = a3) (a1 : A)
: is_equiv (λq : a1 = a2, q ⬝ p) :=
is_equiv.mk (λq, q ⬝ p) (λq, q ⬝ p⁻¹)
(λq, inv_con_cancel_right q p)
(λq, con_inv_cancel_right q p)
(λq, by cases p;cases q;exact idp)
local attribute is_equiv_concat_right [instance]
definition equiv_eq_closed_right (p : a2 = a3) (a1 : A) : (a1 = a2) ≃ (a1 = a3) :=
equiv.mk (λq, q ⬝ p) _
definition eq_equiv_eq_closed (p : a1 = a2) (q : a3 = a4) : (a1 = a3) ≃ (a2 = a4) :=
equiv.trans (equiv_eq_closed_left p a3) (equiv_eq_closed_right q a2)
definition is_equiv_whisker_left (p : a1 = a2) (q r : a2 = a3)
: is_equiv (@whisker_left A a1 a2 a3 p q r) :=
begin
fapply adjointify,
{intro s, apply (!cancel_left s)},
{intro s,
apply concat, {apply whisker_left_con_right},
apply concat, rotate_left 1, apply (whisker_left_inv_left p s),
apply concat2,
{apply concat, {apply whisker_left_con_right},
apply concat2,
{cases p, cases q, apply idp},
{apply idp}},
{cases p, cases r, apply idp}},
{intro s, cases s, cases q, cases p, apply idp}
end
definition eq_equiv_con_eq_con_left (p : a1 = a2) (q r : a2 = a3) : (q = r) ≃ (p ⬝ q = p ⬝ r) :=
equiv.mk _ !is_equiv_whisker_left
definition is_equiv_whisker_right {p q : a1 = a2} (r : a2 = a3)
: is_equiv (λs, @whisker_right A a1 a2 a3 p q s r) :=
begin
fapply adjointify,
{intro s, apply (!cancel_right s)},
{intro s, cases r, cases s, cases q, reflexivity},
{intro s, cases s, cases r, cases p, reflexivity}
end
definition eq_equiv_con_eq_con_right (p q : a1 = a2) (r : a2 = a3) : (p = q) ≃ (p ⬝ r = q ⬝ r) :=
equiv.mk _ !is_equiv_whisker_right
definition is_equiv_con_eq_of_eq_inv_con (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: is_equiv (con_eq_of_eq_inv_con : p = r⁻¹ ⬝ q → r ⬝ p = q) :=
begin
cases r,
apply (@is_equiv_compose _ _ _ _ _ !is_equiv_concat_left !is_equiv_concat_right),
end
definition eq_inv_con_equiv_con_eq (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: (p = r⁻¹ ⬝ q) ≃ (r ⬝ p = q) :=
equiv.mk _ !is_equiv_con_eq_of_eq_inv_con
definition is_equiv_con_eq_of_eq_con_inv (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: is_equiv (con_eq_of_eq_con_inv : r = q ⬝ p⁻¹ → r ⬝ p = q) :=
begin
cases p,
apply (@is_equiv_compose _ _ _ _ _ !is_equiv_concat_left !is_equiv_concat_right)
end
definition eq_con_inv_equiv_con_eq (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: (r = q ⬝ p⁻¹) ≃ (r ⬝ p = q) :=
equiv.mk _ !is_equiv_con_eq_of_eq_con_inv
definition is_equiv_inv_con_eq_of_eq_con (p : a1 = a3) (q : a2 = a3) (r : a1 = a2)
: is_equiv (inv_con_eq_of_eq_con : p = r ⬝ q → r⁻¹ ⬝ p = q) :=
begin
cases r,
apply (@is_equiv_compose _ _ _ _ _ !is_equiv_concat_left !is_equiv_concat_right)
end
definition eq_con_equiv_inv_con_eq (p : a1 = a3) (q : a2 = a3) (r : a1 = a2)
: (p = r ⬝ q) ≃ (r⁻¹ ⬝ p = q) :=
equiv.mk _ !is_equiv_inv_con_eq_of_eq_con
definition is_equiv_con_inv_eq_of_eq_con (p : a3 = a1) (q : a2 = a3) (r : a2 = a1)
: is_equiv (con_inv_eq_of_eq_con : r = q ⬝ p → r ⬝ p⁻¹ = q) :=
begin
cases p,
apply (@is_equiv_compose _ _ _ _ _ !is_equiv_concat_left !is_equiv_concat_right)
end
definition eq_con_equiv_con_inv_eq (p : a3 = a1) (q : a2 = a3) (r : a2 = a1)
: (r = q ⬝ p) ≃ (r ⬝ p⁻¹ = q) :=
equiv.mk _ !is_equiv_con_inv_eq_of_eq_con
definition is_equiv_eq_con_of_inv_con_eq (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: is_equiv (eq_con_of_inv_con_eq : r⁻¹ ⬝ q = p → q = r ⬝ p) :=
begin
cases r,
apply (@is_equiv_compose _ _ _ _ _ !is_equiv_concat_left !is_equiv_concat_right)
end
definition inv_con_eq_equiv_eq_con (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: (r⁻¹ ⬝ q = p) ≃ (q = r ⬝ p) :=
equiv.mk _ !is_equiv_eq_con_of_inv_con_eq
definition is_equiv_eq_con_of_con_inv_eq (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: is_equiv (eq_con_of_con_inv_eq : q ⬝ p⁻¹ = r → q = r ⬝ p) :=
begin
cases p,
apply (@is_equiv_compose _ _ _ _ _ !is_equiv_concat_left !is_equiv_concat_right)
end
definition con_inv_eq_equiv_eq_con (p : a1 = a3) (q : a2 = a3) (r : a2 = a1)
: (q ⬝ p⁻¹ = r) ≃ (q = r ⬝ p) :=
equiv.mk _ !is_equiv_eq_con_of_con_inv_eq
-- a lot of this library still needs to be ported from Coq HoTT
end eq