-- Authors: Floris van Doorn

/-
  In this file we define the smash type. This is the cofiber of the map
    wedge A B → A × B
  However, we define it (equivalently) as the pushout of the maps A + B → 2 and A + B → A × B.
-/

import homotopy.circle homotopy.join types.pointed ..move_to_lib

open bool pointed eq equiv is_equiv sum bool prod unit circle

namespace smash

  variables {A B : Type*}

  section
  open pushout

  definition prod_of_sum [unfold 3] (u : A + B) : A × B :=
  by induction u with a b; exact (a, pt); exact (pt, b)

  definition bool_of_sum [unfold 3] (u : A + B) : bool :=
  by induction u; exact ff; exact tt

  definition smash' (A B : Type*) : Type := pushout (@prod_of_sum A B) (@bool_of_sum A B)
  protected definition mk (a : A) (b : B) : smash' A B := inl (a, b)

  definition smash [constructor] (A B : Type*) : Type* :=
  pointed.MK (smash' A B) (smash.mk pt pt)

  definition auxl : smash A B := inr ff
  definition auxr : smash A B := inr tt
  definition gluel (a : A) : smash.mk a pt = auxl :> smash A B := glue (inl a)
  definition gluer (b : B) : smash.mk pt b = auxr :> smash A B := glue (inr b)

  end

  definition gluel' (a a' : A) : smash.mk a pt = smash.mk a' pt :> smash A B :=
  gluel a ⬝ (gluel a')⁻¹
  definition gluer' (b b' : B) : smash.mk pt b = smash.mk pt b' :> smash A B :=
  gluer b ⬝ (gluer b')⁻¹
  definition glue (a : A) (b : B) : smash.mk a pt = smash.mk pt b :=
  gluel' a pt ⬝ gluer' pt b

  definition glue_pt_left (b : B) : glue (Point A) b = gluer' pt b :=
  whisker_right !con.right_inv _ ⬝ !idp_con

  definition glue_pt_right (a : A) : glue a (Point B) = gluel' a pt :=
  proof whisker_left _ !con.right_inv qed

  definition ap_mk_left {a a' : A} (p : a = a') : ap (λa, smash.mk a (Point B)) p = gluel' a a' :=
  by induction p; exact !con.right_inv⁻¹

  definition ap_mk_right {b b' : B} (p : b = b') : ap (smash.mk (Point A)) p = gluer' b b' :=
  by induction p; exact !con.right_inv⁻¹

  protected definition rec {P : smash A B → Type} (Pmk : Πa b, P (smash.mk a b))
    (Pl : P auxl) (Pr : P auxr) (Pgl : Πa, Pmk a pt =[gluel a] Pl)
    (Pgr : Πb, Pmk pt b =[gluer b] Pr) (x : smash' A B) : P x :=
  begin
    induction x with x b u,
    { induction x with a b, exact Pmk a b },
    { induction b, exact Pl, exact Pr },
    { induction u: esimp,
      { apply Pgl },
      { apply Pgr }}
  end

  -- a rec which is easier to prove, but with worse computational properties
  protected definition rec' {P : smash A B → Type} (Pmk : Πa b, P (smash.mk a b))
    (Pg : Πa b, Pmk a pt =[glue a b] Pmk pt b) (x : smash' A B) : P x :=
  begin
    induction x using smash.rec,
    { apply Pmk },
    { exact gluel pt ▸ Pmk pt pt },
    { exact gluer pt ▸ Pmk pt pt },
    { refine change_path _ (Pg a pt ⬝o !pathover_tr),
      refine whisker_right !glue_pt_right _ ⬝ _, esimp, refine !con.assoc ⬝ _,
      apply whisker_left, apply con.left_inv },
    { refine change_path _ ((Pg pt b)⁻¹ᵒ ⬝o !pathover_tr),
      refine whisker_right !glue_pt_left⁻² _ ⬝ _,
      refine whisker_right !inv_con_inv_right _ ⬝ _, refine !con.assoc ⬝ _,
      apply whisker_left, apply con.left_inv }
  end

  theorem rec_gluel {P : smash A B → Type} {Pmk : Πa b, P (smash.mk a b)}
    {Pl : P auxl} {Pr : P auxr} (Pgl : Πa, Pmk a pt =[gluel a] Pl)
    (Pgr : Πb, Pmk pt b =[gluer b] Pr) (a : A) :
    apd (smash.rec Pmk Pl Pr Pgl Pgr) (gluel a) = Pgl a :=
  !pushout.rec_glue

  theorem rec_gluer {P : smash A B → Type} {Pmk : Πa b, P (smash.mk a b)}
    {Pl : P auxl} {Pr : P auxr} (Pgl : Πa, Pmk a pt =[gluel a] Pl)
    (Pgr : Πb, Pmk pt b =[gluer b] Pr) (b : B) :
    apd (smash.rec Pmk Pl Pr Pgl Pgr) (gluer b) = Pgr b :=
  !pushout.rec_glue

  theorem rec_glue {P : smash A B → Type} {Pmk : Πa b, P (smash.mk a b)}
    {Pl : P auxl} {Pr : P auxr} (Pgl : Πa, Pmk a pt =[gluel a] Pl)
    (Pgr : Πb, Pmk pt b =[gluer b] Pr) (a : A) (b : B) :
    apd (smash.rec Pmk Pl Pr Pgl Pgr) (glue a b) =
      (Pgl a ⬝o (Pgl pt)⁻¹ᵒ) ⬝o (Pgr pt ⬝o (Pgr b)⁻¹ᵒ) :=
  by rewrite [↑glue, ↑gluel', ↑gluer', +apd_con, +apd_inv, +rec_gluel, +rec_gluer]

  protected definition elim {P : Type} (Pmk : Πa b, P) (Pl Pr : P)
    (Pgl : Πa : A, Pmk a pt = Pl) (Pgr : Πb : B, Pmk pt b = Pr) (x : smash' A B) : P :=
  smash.rec Pmk Pl Pr (λa, pathover_of_eq _ (Pgl a)) (λb, pathover_of_eq _ (Pgr b)) x

  -- an elim which is easier to prove, but with worse computational properties
  protected definition elim' {P : Type} (Pmk : Πa b, P) (Pg : Πa b, Pmk a pt = Pmk pt b)
    (x : smash' A B) : P :=
  smash.rec' Pmk (λa b, pathover_of_eq _ (Pg a b)) x

  theorem elim_gluel {P : Type} {Pmk : Πa b, P} {Pl Pr : P}
    (Pgl : Πa : A, Pmk a pt = Pl) (Pgr : Πb : B, Pmk pt b = Pr) (a : A) :
    ap (smash.elim Pmk Pl Pr Pgl Pgr) (gluel a) = Pgl a :=
  begin
    apply eq_of_fn_eq_fn_inv !(pathover_constant (@gluel A B a)),
    rewrite [▸*,-apd_eq_pathover_of_eq_ap,↑smash.elim,rec_gluel],
  end

  theorem elim_gluer {P : Type} {Pmk : Πa b, P} {Pl Pr : P}
    (Pgl : Πa : A, Pmk a pt = Pl) (Pgr : Πb : B, Pmk pt b = Pr) (b : B) :
    ap (smash.elim Pmk Pl Pr Pgl Pgr) (gluer b) = Pgr b :=
  begin
    apply eq_of_fn_eq_fn_inv !(pathover_constant (@gluer A B b)),
    rewrite [▸*,-apd_eq_pathover_of_eq_ap,↑smash.elim,rec_gluer],
  end

  theorem elim_glue {P : Type} {Pmk : Πa b, P} {Pl Pr : P}
    (Pgl : Πa : A, Pmk a pt = Pl) (Pgr : Πb : B, Pmk pt b = Pr) (a : A) (b : B) :
    ap (smash.elim Pmk Pl Pr Pgl Pgr) (glue a b) = (Pgl a ⬝ (Pgl pt)⁻¹) ⬝ (Pgr pt ⬝ (Pgr b)⁻¹) :=
  by rewrite [↑glue, ↑gluel', ↑gluer', +ap_con, +ap_inv, +elim_gluel, +elim_gluer]

end smash
open smash
attribute smash.mk auxl auxr [constructor]
attribute smash.rec smash.elim [unfold 9] [recursor 9]
attribute smash.rec' smash.elim' [unfold 6]

namespace smash

  variables {A B : Type*}

  definition of_smash_pbool [unfold 2] (x : smash A pbool) : A :=
  begin
    induction x,
    { induction b, exact pt, exact a },
    { exact pt },
    { exact pt },
    { reflexivity },
    { induction b: reflexivity }
  end

  definition smash_pbool_equiv [constructor] (A : Type*) : smash A pbool ≃* A :=
  begin
    fapply pequiv_of_equiv,
    { fapply equiv.MK,
      { exact of_smash_pbool },
      { intro a, exact smash.mk a tt },
      { intro a, reflexivity },
      { exact abstract begin intro x, induction x using smash.rec',
        { induction b, exact (glue a tt)⁻¹, reflexivity },
        { apply eq_pathover_id_right, induction b: esimp,
          { refine ap02 _ !glue_pt_right ⬝ph _,
            refine ap_compose (λx, smash.mk x _) _ _ ⬝ph _,
            refine ap02 _ (!ap_con ⬝ (!elim_gluel ◾ (!ap_inv ⬝ !elim_gluel⁻²))) ⬝ph _,
            apply hinverse, apply square_of_eq,
            esimp, refine (!glue_pt_right ◾ !glue_pt_left)⁻¹ },
          { apply square_of_eq, refine !con.left_inv ⬝ _, esimp, symmetry,
            refine ap_compose (λx, smash.mk x _) _ _ ⬝ _,
            exact ap02 _ !elim_glue }} end end }},
    { reflexivity }
  end

  /- smash A (susp B) = susp (smash A B) <- this follows from associativity and smash with S¹-/

  /- To prove: Σ(X × Y) ≃ ΣX ∨ ΣY ∨ Σ(X ∧ Y) (notation means suspension, wedge, smash),
     and both are equivalent to the reduced join -/

  /- To prove: commutative, associative -/

  /- smash A S¹ = susp A -/
  open susp

  definition psusp_of_smash_pcircle [unfold 2] (x : smash A S¹*) : psusp A :=
  begin
    induction x,
    { induction b, exact pt, exact merid a ⬝ (merid pt)⁻¹ },
    { exact pt },
    { exact pt },
    { reflexivity },
    { induction b, reflexivity, apply eq_pathover_constant_right, apply hdeg_square,
      exact !elim_loop ⬝ !con.right_inv }
  end

  definition smash_pcircle_of_psusp [unfold 2] (x : psusp A) : smash A S¹* :=
  begin
    induction x,
    { exact pt },
    { exact pt },
    { exact gluel' pt a ⬝ ap (smash.mk a) loop ⬝ gluel' a pt },
  end

exit -- the definitions below compile, but take a long time to do so and have sorry's in them
  definition smash_pcircle_of_psusp_of_smash_pcircle_pt [unfold 3] (a : A) (x : S¹*) :
    smash_pcircle_of_psusp (psusp_of_smash_pcircle (smash.mk a x)) = smash.mk a x :=
  begin
    induction x,
    { exact gluel' pt a },
    { exact abstract begin apply eq_pathover,
      refine ap_compose smash_pcircle_of_psusp _ _ ⬝ph _,
      refine ap02 _ (elim_loop north (merid a ⬝ (merid pt)⁻¹)) ⬝ph _,
      refine !ap_con ⬝ (!elim_merid ◾ (!ap_inv ⬝ !elim_merid⁻²)) ⬝ph _,
      -- make everything below this a lemma defined by path induction?
      apply square_of_eq, rewrite [+con.assoc], apply whisker_left, apply whisker_left,
      symmetry, apply con_eq_of_eq_inv_con, esimp, apply con_eq_of_eq_con_inv,
      refine _⁻² ⬝ !con_inv, refine _ ⬝ !con.assoc,
      refine _ ⬝ whisker_right !inv_con_cancel_right⁻¹ _, refine _ ⬝ !con.right_inv⁻¹,
      refine !con.right_inv ◾ _, refine _ ◾ !con.right_inv,
      refine !ap_mk_right ⬝ !con.right_inv end end }
  end

  definition smash_pcircle_of_psusp_of_smash_pcircle_gluer_base (b : S¹*)
    : square (smash_pcircle_of_psusp_of_smash_pcircle_pt (Point A) b)
             (gluer pt)
             (ap smash_pcircle_of_psusp (ap (λ a, psusp_of_smash_pcircle a) (gluer b)))
             (gluer b) :=
  begin
    refine ap02 _ !elim_gluer ⬝ph _,
    induction b,
    { apply square_of_eq, exact whisker_right !con.right_inv _ },
    { apply square_pathover', exact sorry }
  end

  definition smash_pcircle_pequiv [constructor] (A : Type*) : smash A S¹* ≃* psusp A :=
  begin
    fapply pequiv_of_equiv,
    { fapply equiv.MK,
      { exact psusp_of_smash_pcircle },
      { exact smash_pcircle_of_psusp },
      { exact abstract begin intro x, induction x,
        { reflexivity },
        { exact merid pt },
        { apply eq_pathover_id_right,
          refine ap_compose psusp_of_smash_pcircle _ _ ⬝ph _,
          refine ap02 _ !elim_merid ⬝ph _,
          rewrite [↑gluel', +ap_con, +ap_inv, -ap_compose'],
          refine (_ ◾ _⁻² ◾ _ ◾ (_ ◾ _⁻²)) ⬝ph _,
          rotate 5, do 2 apply elim_gluel, esimp, apply elim_loop, do 2 apply elim_gluel,
          refine idp_con (merid a ⬝ (merid (Point A))⁻¹) ⬝ph _,
          apply square_of_eq, refine !idp_con ⬝ _⁻¹, apply inv_con_cancel_right } end end },
      { intro x, induction x using smash.rec,
        { exact smash_pcircle_of_psusp_of_smash_pcircle_pt a b },
        { exact gluel pt },
        { exact gluer pt },
        { apply eq_pathover_id_right,
          refine ap_compose smash_pcircle_of_psusp _ _ ⬝ph _,
          refine ap02 _ !elim_gluel ⬝ph _,
          esimp, apply whisker_rt, exact vrfl },
        { apply eq_pathover_id_right,
          refine ap_compose smash_pcircle_of_psusp _ _ ⬝ph _,
          refine ap02 _ !elim_gluer ⬝ph _,
          induction b,
          { apply square_of_eq, exact whisker_right !con.right_inv _ },
          { exact sorry}
          }}},
    { reflexivity }
  end

end smash
-- (X × A) → Y ≃ X → A → Y