Require Import Basics Types.
[Loading ML file number_string_notation_plugin.cmxs (using legacy method) ... done]
Require Import Pointed WildCat.
Require Import Modalities.ReflectiveSubuniverse Truncations.Core.
Require Import Algebra.AbGroups.
Require Import Homotopy.HomotopyGroup.
Require Import Homotopy.PinSn.
Require Import Spaces.Int.Core Spaces.Circle.

Require Import Spaces.Torus.Torus.
Require Import Spaces.Torus.TorusEquivCircles.

Local Open Scope trunc_scope.
Local Open Scope pointed_scope.

(** ** Fundamental group of the torus .*)

(** The torus is 1-truncated *)

Global Instance is1type_torus `{Univalence} : IsTrunc 1 Torus.
H: Univalence
IsTrunc 1 Torus
Proof.
H: Univalence
IsTrunc 1 Torus
  refine (istrunc_equiv_istrunc _ equiv_torus_prod_Circle^-1).
Qed.

(** The torus is 0-connected *)

Global Instance isconnected_torus `{Univalence} : IsConnected 0 Torus.
H: Univalence
IsConnected (Tr 0) Torus
Proof.
H: Univalence
IsConnected (Tr 0) Torus
  srapply (isconnected_equiv' _ _ equiv_torus_prod_Circle^-1).
H: Univalence
IsConnected (Tr 0) (Circle * Circle)
  srapply (isconnected_equiv' _ _ (equiv_sigma_prod0 _ _)).
Qed.

(** We give these notations for the pointed versions. *)
Local Notation T := ([Torus, _]).
Local Notation S1 := ([Circle, _]).

(** A pointed version of the equivalence from TorusEquivCircles.v. *)
(** TODO: If [Funext] is removed from there, remove it from here as well. *)
Lemma pequiv_torus_prod_circles `{Funext} : T  <~>* S1 * S1.
H: Funext
T <~>* S1 * S1
Proof.
H: Funext
T <~>* S1 * S1
  srapply Build_pEquiv'.
H: Funext
T <~> [S1 * S1, ispointed_prod]
H: Funext
?f pt = pt
  1: apply equiv_torus_prod_Circle.
H: Funext
equiv_torus_prod_Circle pt = pt
  reflexivity.
Defined.

(** Fundamental group of torus *)
Theorem pi1_torus `{Univalence}
  : GroupIsomorphism (Pi 1 T) (grp_prod abgroup_Z abgroup_Z).
H: Univalence
GroupIsomorphism (Pi 1 T)
  (grp_prod abgroup_Z abgroup_Z)
Proof.
H: Univalence
GroupIsomorphism (Pi 1 T)
  (grp_prod abgroup_Z abgroup_Z)
  etransitivity.
H: Univalence
GroupIsomorphism (Pi 1 T) ?Goal
H: Univalence
GroupIsomorphism ?Goal (grp_prod abgroup_Z abgroup_Z)
  1: exact (emap (Pi 1) pequiv_torus_prod_circles).
H: Univalence
GroupIsomorphism (Pi 1 (S1 * S1))
  (grp_prod abgroup_Z abgroup_Z)
  etransitivity.
H: Univalence
GroupIsomorphism (Pi 1 (S1 * S1)) ?Goal
H: Univalence
GroupIsomorphism ?Goal (grp_prod abgroup_Z abgroup_Z)
  1: apply grp_iso_pi_prod.
H: Univalence
GroupIsomorphism (grp_prod (Pi 1 S1) (Pi 1 S1))
  (grp_prod abgroup_Z abgroup_Z)
  apply grp_iso_prod.
H: Univalence
Pi 1 S1 $<~> abgroup_Z
H: Univalence
Pi 1 S1 $<~> abgroup_Z
  1,2: apply pi1_circle.
Defined.

(** Loop space of torus *)
Theorem loops_torus `{Univalence} : loops T <~>* Int * Int.
H: Univalence
loops T <~>* Int * Int
Proof.
H: Univalence
loops T <~>* Int * Int
  (* Since [T] is 1-truncated, [loops T] is 0-truncated, and is therefore equivalent to its 0-truncation. *)
  refine (_ o*E pequiv_ptr (n:=0)).
H: Univalence
pTr 0 (loops T) <~>* Int * Int
  nrapply pi1_torus.
Defined.