131 lines
6.3 KiB
Text
131 lines
6.3 KiB
Text
/-
|
|
Copyright (c) 2015 Floris van Doorn. All rights reserved.
|
|
Released under Apache 2.0 license as described in the file LICENSE.
|
|
|
|
Module: types.square
|
|
Author: Floris van Doorn
|
|
|
|
Theorems about square
|
|
-/
|
|
|
|
open eq equiv is_equiv
|
|
|
|
namespace cubical
|
|
|
|
variables {A : Type} {a a' a'' a₀₀ a₂₀ a₄₀ a₀₂ a₂₂ a₂₄ a₀₄ a₄₂ a₄₄ : A}
|
|
/-a₀₀-/ {p₁₀ : a₀₀ = a₂₀} /-a₂₀-/ {p₃₀ : a₂₀ = a₄₀} /-a₄₀-/
|
|
{p₀₁ : a₀₀ = a₀₂} /-s₁₁-/ {p₂₁ : a₂₀ = a₂₂} /-s₃₁-/ {p₄₁ : a₄₀ = a₄₂}
|
|
/-a₀₂-/ {p₁₂ : a₀₂ = a₂₂} /-a₂₂-/ {p₃₂ : a₂₂ = a₄₂} /-a₄₂-/
|
|
{p₀₃ : a₀₂ = a₀₄} /-s₁₃-/ {p₂₃ : a₂₂ = a₂₄} /-s₃₃-/ {p₄₃ : a₄₂ = a₄₄}
|
|
/-a₀₄-/ {p₁₄ : a₀₄ = a₂₄} /-a₂₄-/ {p₃₄ : a₂₄ = a₄₄} /-a₄₄-/
|
|
|
|
|
|
inductive square {A : Type} {a₀₀ : A}
|
|
: Π{a₂₀ a₀₂ a₂₂ : A}, a₀₀ = a₂₀ → a₀₂ = a₂₂ → a₀₀ = a₀₂ → a₂₀ = a₂₂ → Type :=
|
|
ids : square idp idp idp idp
|
|
/- square top bottom left right -/
|
|
|
|
variables {s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁} {s₃₁ : square p₃₀ p₃₂ p₂₁ p₄₁}
|
|
{s₁₃ : square p₁₂ p₁₄ p₀₃ p₂₃} {s₃₃ : square p₃₂ p₃₄ p₂₃ p₄₃}
|
|
|
|
definition ids [reducible] := @square.ids
|
|
definition idsquare [reducible] (a : A) := @square.ids A a
|
|
|
|
definition hrefl (p : a = a') : square idp idp p p :=
|
|
by cases p; exact ids
|
|
|
|
definition vrefl (p : a = a') : square p p idp idp :=
|
|
by cases p; exact ids
|
|
|
|
definition hconcat (s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁) (s₃₁ : square p₃₀ p₃₂ p₂₁ p₄₁)
|
|
: square (p₁₀ ⬝ p₃₀) (p₁₂ ⬝ p₃₂) p₀₁ p₄₁ :=
|
|
by cases s₃₁; exact s₁₁
|
|
|
|
definition vconcat (s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁) (s₁₃ : square p₁₂ p₁₄ p₀₃ p₂₃)
|
|
: square p₁₀ p₁₄ (p₀₁ ⬝ p₀₃) (p₂₁ ⬝ p₂₃) :=
|
|
by cases s₁₃; exact s₁₁
|
|
|
|
definition hinverse (s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁) : square p₁₀⁻¹ p₁₂⁻¹ p₂₁ p₀₁ :=
|
|
by cases s₁₁;exact ids
|
|
|
|
definition vinverse (s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁) : square p₁₂ p₁₀ p₀₁⁻¹ p₂₁⁻¹ :=
|
|
by cases s₁₁;exact ids
|
|
|
|
definition transpose (s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁) : square p₀₁ p₂₁ p₁₀ p₁₂ :=
|
|
by cases s₁₁;exact ids
|
|
|
|
definition eq_of_square (s₁₁ : square p₁₀ p₁₂ p₀₁ p₂₁) : p₁₀ ⬝ p₂₁ = p₀₁ ⬝ p₁₂ :=
|
|
by cases s₁₁; apply idp
|
|
|
|
definition hdegen_square {p q : a = a'} (r : p = q) : square idp idp p q :=
|
|
by cases r;apply hrefl
|
|
|
|
definition vdegen_square {p q : a = a'} (r : p = q) : square p q idp idp :=
|
|
by cases r;apply vrefl
|
|
|
|
definition square_of_eq (r : p₁₀ ⬝ p₂₁ = p₀₁ ⬝ p₁₂) : square p₁₀ p₁₂ p₀₁ p₂₁ :=
|
|
by cases p₁₂; (esimp [concat] at r); cases r; cases p₂₁; cases p₁₀; exact ids
|
|
|
|
definition square_equiv_eq (t : a₀₀ = a₀₂) (b : a₂₀ = a₂₂) (l : a₀₀ = a₂₀) (r : a₀₂ = a₂₂)
|
|
: square t b l r ≃ t ⬝ r = l ⬝ b :=
|
|
begin
|
|
fapply equiv.MK,
|
|
{ exact eq_of_square},
|
|
{ exact square_of_eq},
|
|
{ intro s, cases b, esimp [concat] at s, cases s, cases r, cases t, apply idp},
|
|
{ intro s, cases s, apply idp},
|
|
end
|
|
|
|
definition rec_on_b {a₀₀ : A}
|
|
{P : Π{a₂₀ a₁₂ : A} {t : a₀₀ = a₂₀} {l : a₀₀ = a₁₂} {r : a₂₀ = a₁₂}, square t idp l r → Type}
|
|
{a₂₀ a₁₂ : A} {t : a₀₀ = a₂₀} {l : a₀₀ = a₁₂} {r : a₂₀ = a₁₂}
|
|
(s : square t idp l r) (H : P ids) : P s :=
|
|
have H2 : P (square_of_eq (eq_of_square s)),
|
|
from eq.rec_on (eq_of_square s : t ⬝ r = l) (by cases r; cases t; exact H),
|
|
left_inv (to_fun !square_equiv_eq) s ▹ H2
|
|
|
|
definition rec_on_r {a₀₀ : A}
|
|
{P : Π{a₀₂ a₂₁ : A} {t : a₀₀ = a₂₁} {b : a₀₂ = a₂₁} {l : a₀₀ = a₀₂}, square t b l idp → Type}
|
|
{a₀₂ a₂₁ : A} {t : a₀₀ = a₂₁} {b : a₀₂ = a₂₁} {l : a₀₀ = a₀₂}
|
|
(s : square t b l idp) (H : P ids) : P s :=
|
|
let p : l ⬝ b = t := (eq_of_square s)⁻¹ in
|
|
have H2 : P (square_of_eq (eq_of_square s)⁻¹⁻¹),
|
|
from @eq.rec_on _ _ (λx p, P (square_of_eq p⁻¹)) _ p (by cases b; cases l; exact H),
|
|
left_inv (to_fun !square_equiv_eq) s ▹ !inv_inv ▹ H2
|
|
|
|
definition rec_on_l {a₀₁ : A}
|
|
{P : Π {a₂₀ a₂₂ : A} {t : a₀₁ = a₂₀} {b : a₀₁ = a₂₂} {r : a₂₀ = a₂₂},
|
|
square t b idp r → Type}
|
|
{a₂₀ a₂₂ : A} {t : a₀₁ = a₂₀} {b : a₀₁ = a₂₂} {r : a₂₀ = a₂₂}
|
|
(s : square t b idp r) (H : P ids) : P s :=
|
|
let p : t ⬝ r = b := eq_of_square s ⬝ !idp_con in
|
|
have H2 : P (square_of_eq (p ⬝ !idp_con⁻¹)),
|
|
from eq.rec_on p (by cases r; cases t; exact H),
|
|
left_inv (to_fun !square_equiv_eq) s ▹ !con_inv_cancel_right ▹ H2
|
|
|
|
definition rec_on_t {a₁₀ : A}
|
|
{P : Π {a₀₂ a₂₂ : A} {b : a₀₂ = a₂₂} {l : a₁₀ = a₀₂} {r : a₁₀ = a₂₂}, square idp b l r → Type}
|
|
{a₀₂ a₂₂ : A} {b : a₀₂ = a₂₂} {l : a₁₀ = a₀₂} {r : a₁₀ = a₂₂}
|
|
(s : square idp b l r) (H : P ids) : P s :=
|
|
let p : l ⬝ b = r := (eq_of_square s)⁻¹ ⬝ !idp_con in
|
|
assert H2 : P (square_of_eq ((p ⬝ !idp_con⁻¹)⁻¹)),
|
|
from eq.rec_on p (by cases b; cases l; exact H),
|
|
assert H3 : P (square_of_eq ((eq_of_square s)⁻¹⁻¹)),
|
|
from eq.rec_on !con_inv_cancel_right H2,
|
|
assert H4 : P (square_of_eq (eq_of_square s)),
|
|
from eq.rec_on !inv_inv H3,
|
|
proof
|
|
left_inv (to_fun !square_equiv_eq) s ▹ H4
|
|
qed
|
|
|
|
definition rec_on_tb {a : A}
|
|
{P : Π{b : A} {l : a = b} {r : a = b}, square idp idp l r → Type}
|
|
{b : A} {l : a = b} {r : a = b}
|
|
(s : square idp idp l r) (H : P ids) : P s :=
|
|
have H2 : P (square_of_eq (eq_of_square s)),
|
|
from eq.rec_on (eq_of_square s : idp ⬝ r = l) (by cases r; exact H),
|
|
left_inv (to_fun !square_equiv_eq) s ▹ H2
|
|
|
|
--we can also do the other recursors (lr, tl, tr, bl, br, tbl, tbr, tlr, blr), but let's postpone this until they are needed
|
|
|
|
end cubical
|