import Mathlib
import Analysis.Section_3_1
import Analysis.Tags.Section_3_1
import Analysis.Tools.ExistsUnique

namespace Chapter3

-- <CONTEXT>
universe u v

class SetTheory where
  Set : Type u
  Object : Type v
  set_to_object : Set ↪ Object
  mem : Object → Set → Prop
  extensionality X Y : (∀ x, mem x X ↔ mem x Y) → X = Y
  emptyset: Set
  emptyset_mem x : ¬ mem x emptyset
  singleton : Object → Set
  singleton_axiom x y : mem x (singleton y) ↔ x = y
  union_pair : Set → Set → Set
  union_pair_axiom X Y x : mem x (union_pair X Y) ↔ (mem x X ∨ mem x Y)
  specify A (P: Subtype (mem . A) → Prop) : Set
  specification_axiom A (P: Subtype (mem . A) → Prop) :
    (∀ x, mem x (specify A P) → mem x A) ∧ ∀ x, mem x.val (specify A P) ↔ P x
  replace A (P: Subtype (mem . A) → Object → Prop)
    (hP: ∀ x y y', P x y ∧ P x y' → y = y') : Set
  replacement_axiom A (P: Subtype (mem . A) → Object → Prop)
    (hP: ∀ x y y', P x y ∧ P x y' → y = y') : ∀ y, mem y (replace A P hP) ↔ ∃ x, P x y
  nat : Set
  nat_equiv : ℕ ≃ Subtype (mem . nat)
  regularity_axiom A (hA : ∃ x, mem x A) :
    ∃ x, mem x A ∧ ∀ S, x = set_to_object S → ¬ ∃ y, mem y A ∧ mem y S
  pow : Set → Set → Set
  function_to_object (X: Set) (Y: Set) :
    (Subtype (mem . X) → Subtype (mem . Y)) ↪ Object
  powerset_axiom (X: Set) (Y: Set) (F:Object) :
    mem F (pow X Y) ↔ ∃ f: Subtype (mem . Y) → Subtype (mem . X),
    function_to_object Y X f = F
  union : Set → Set
  union_axiom A x : mem x (union A) ↔ ∃ S, mem x S ∧ mem (set_to_object S) A

export SetTheory (Set Object)

variable [SetTheory]

instance SetTheory.objects_mem_sets : Membership Object Set where
  mem X x := mem x X

instance SetTheory.sets_are_objects : Coe Set Object where
  coe X := SetTheory.set_to_object X

theorem SetTheory.Set.coe_eq {X Y:Set} (h: (X: Object) = (Y: Object)) : X = Y :=
  SetTheory.set_to_object.inj' h

@[simp]
theorem SetTheory.Set.coe_eq_iff (X Y:Set) : (X: Object) = (Y: Object) ↔  X = Y := by
  sorry

@[ext]
theorem SetTheory.Set.ext {X Y:Set} (h: ∀ x, x ∈ X ↔ x ∈ Y) : X = Y := SetTheory.extensionality _ _ h

instance SetTheory.Set.instEmpty : EmptyCollection Set where
  emptyCollection := SetTheory.emptyset

@[simp]
theorem SetTheory.Set.not_mem_empty : ∀ x, x ∉ (∅:Set) := SetTheory.emptyset_mem

instance SetTheory.Set.instSingleton : Singleton Object Set where
  singleton := SetTheory.singleton

@[simp]
theorem SetTheory.Set.mem_singleton (x a:Object) : x ∈ ({a}:Set) ↔ x = a := SetTheory.singleton_axiom x a

instance SetTheory.Set.instUnion : Union Set where
  union := SetTheory.union_pair

@[simp]
theorem SetTheory.Set.mem_union (x:Object) (X Y:Set) : x ∈ (X ∪ Y) ↔ (x ∈ X ∨ x ∈ Y) :=
  SetTheory.union_pair_axiom X Y x

abbrev SetTheory.Set.toSubtype (A:Set) := Subtype (fun x ↦ x ∈ A)

instance : CoeSort (Set) (Type v) where
  coe A := A.toSubtype

abbrev SetTheory.Set.specify (A:Set) (P: A → Prop) : Set := SetTheory.specify A P

theorem SetTheory.Set.specification_axiom {A:Set} {P: A → Prop} {x:Object} (h: x ∈ A.specify P) :
    x ∈ A :=
  (SetTheory.specification_axiom A P).1 x h

theorem SetTheory.Set.specification_axiom' {A:Set} (P: A → Prop) (x:A) :
    x.val ∈ A.specify P ↔ P x :=
  (SetTheory.specification_axiom A P).2 x

@[simp]
theorem SetTheory.Set.specification_axiom'' {A:Set} (P: A → Prop) (x:Object) :
    x ∈ A.specify P ↔ ∃ h:x ∈ A, P ⟨ x, h ⟩ := by
  sorry

instance SetTheory.Set.instSDiff : SDiff Set where
  sdiff X Y := X.specify (fun x ↦ x.val ∉ Y)

@[simp]
theorem SetTheory.Set.mem_sdiff (x:Object) (X Y:Set) : x ∈ (X \ Y) ↔ (x ∈ X ∧ x ∉ Y) := by
  sorry

abbrev Nat := SetTheory.nat

def SetTheory.Set.nat_equiv : ℕ ≃ Nat := SetTheory.nat_equiv

instance SetTheory.Set.instOfNat {n:ℕ} : OfNat Nat n where
  ofNat := nat_equiv n

instance SetTheory.Set.instNatCast : NatCast Nat where
  natCast n := nat_equiv n

instance SetTheory.Set.toNat : Coe Nat ℕ where
  coe n := nat_equiv.symm n

instance SetTheory.Object.instNatCast : NatCast Object where
  natCast n := (n:Nat).val

instance SetTheory.Object.instOfNat {n:ℕ} : OfNat Object n where
  ofNat := ((n:Nat):Object)

@[simp]
lemma SetTheory.Object.ofnat_eq {n:ℕ} : ((n:Nat):Object) = (n:Object) := rfl

lemma SetTheory.Object.ofnat_eq' {n:ℕ} : (ofNat(n):Object) = (n:Object) := rfl

@[simp]
theorem SetTheory.Object.natCast_inj (n m:ℕ) :
    (n : Object) = (m : Object) ↔ n = m := by
  sorry

@[simp]
lemma SetTheory.Set.nat_equiv_coe_of_coe (n:ℕ) : ((n:Nat):ℕ) = n :=
  Equiv.symm_apply_apply nat_equiv n

noncomputable def ExistsUnique.choose {α: Sort*} {p: α → Prop} (h : ∃! x, p x) : α := h.exists.choose

@[ext]
structure Function (X Y: Set) where
  P : X → Y → Prop
  unique : ∀ x: X, ∃! y: Y, P x y

#check Function.mk

noncomputable def Function.to_fn {X Y: Set} (f: Function X Y) : X → Y :=
  fun x ↦ (f.unique x).choose

noncomputable instance Function.inst_coefn (X Y: Set) : CoeFun (Function X Y) (fun _ ↦ X → Y) where
  coe := Function.to_fn

theorem Function.to_fn_eval {X Y: Set} (f: Function X Y) (x:X) : f.to_fn x = f x := by
  sorry

abbrev Function.mk_fn {X Y: Set} (f: X → Y) : Function X Y :=
  Function.mk (fun x y ↦ y = f x) (by simp)

theorem Function.eval {X Y: Set} (f: Function X Y) (x: X) (y: Y) : y = f x ↔ f.P x y := by
  sorry

@[simp]
theorem Function.eval_of {X Y: Set} (f: X → Y) (x:X) : (Function.mk_fn f) x = f x := by
  sorry

abbrev P_3_3_3a : Nat → Nat → Prop := fun x y ↦ (y:ℕ) = (x:ℕ)+1

theorem SetTheory.Set.P_3_3_3a_existsUnique (x: Nat) : ∃! y: Nat, P_3_3_3a x y := by
  sorry

abbrev SetTheory.Set.f_3_3_3a : Function Nat Nat := Function.mk P_3_3_3a P_3_3_3a_existsUnique

theorem SetTheory.Set.f_3_3_3a_eval (x y: Nat) : y = f_3_3_3a x ↔ (y:ℕ) = (x+1:ℕ) := by
  sorry

theorem SetTheory.Set.f_3_3_3a_eval' (n: ℕ) : f_3_3_3a (n:Nat) = (n+1:ℕ) := by
  sorry

theorem SetTheory.Set.f_3_3_3a_eval'' : f_3_3_3a 4 = 5 := by
  sorry

theorem SetTheory.Set.f_3_3_3a_eval''' (n:ℕ) : f_3_3_3a (2*n+3: ℕ) = (2*n+4:ℕ) := by
  sorry

abbrev SetTheory.Set.P_3_3_3b : Nat → Nat → Prop := fun x y ↦ (y+1:ℕ) = (x:ℕ)

theorem SetTheory.Set.not_P_3_3_3b_existsUnique : ¬ ∀ x, ∃! y: Nat, P_3_3_3b x y := by
  sorry

abbrev SetTheory.Set.P_3_3_3c : (Nat \ {(0:Object)}: Set) → Nat → Prop :=
  fun x y ↦ ((y+1:ℕ):Object) = x

theorem SetTheory.Set.P_3_3_3c_existsUnique (x: (Nat \ {(0:Object)}: Set)) :
    ∃! y: Nat, P_3_3_3c x y := by
  sorry

abbrev SetTheory.Set.f_3_3_3c : Function (Nat \ {(0:Object)}: Set) Nat :=
  Function.mk P_3_3_3c P_3_3_3c_existsUnique

theorem SetTheory.Set.f_3_3_3c_eval (x: (Nat \ {(0:Object)}: Set)) (y: Nat) :
    y = f_3_3_3c x ↔ ((y+1:ℕ):Object) = x := by
  sorry

abbrev SetTheory.Set.coe_nonzero (n:ℕ) (h: n ≠ 0): (Nat \ {(0:Object)}: Set) :=
  ⟨((n:ℕ):Object), by
    simp [Object.ofnat_eq',h]
    rw [←Object.ofnat_eq]
    exact Subtype.property _
  ⟩

theorem SetTheory.Set.f_3_3_3c_eval' (n: ℕ) : f_3_3_3c (coe_nonzero (n+1) (by positivity)) = n := by
  sorry

theorem SetTheory.Set.f_3_3_3c_eval'' : f_3_3_3c (coe_nonzero 4 (by positivity)) = 3 := by
  sorry

theorem SetTheory.Set.f_3_3_3c_eval''' (n:ℕ) :
    f_3_3_3c (coe_nonzero (2*n+3) (by positivity)) = (2*n+2:ℕ) := by
  sorry

abbrev SetTheory.Set.P_3_3_5 : Nat → Nat → Prop := fun _x y ↦ y = 7

theorem SetTheory.Set.P_3_3_5_existsUnique (x: Nat) : ∃! y: Nat, P_3_3_5 x y := by
  sorry

abbrev SetTheory.Set.f_3_3_5 : Function Nat Nat := Function.mk P_3_3_5 P_3_3_5_existsUnique

theorem SetTheory.Set.f_3_3_5_eval (x: Nat) : f_3_3_5 x = 7 := by
  sorry

theorem Function.eq_iff {X Y: Set} (f g: Function X Y) : f = g ↔ ∀ x: X, f x = g x := by
  sorry

abbrev SetTheory.Set.f_3_3_10a : Function Nat Nat := Function.mk_fn (fun x ↦ (x^2 + 2*x + 1:ℕ))

abbrev SetTheory.Set.f_3_3_10b : Function Nat Nat := Function.mk_fn (fun x ↦ ((x+1)^2:ℕ))

theorem SetTheory.Set.f_3_3_10_eq : f_3_3_10a = f_3_3_10b := by
  sorry

abbrev SetTheory.Set.f_3_3_11 (X:Set) : Function (∅:Set) X :=
  Function.mk (fun _ _ ↦ True) (by intro ⟨ x,hx ⟩; simp at hx)

theorem SetTheory.Set.empty_function_unique {X: Set} (f g: Function (∅:Set) X) : f = g := by
  sorry

noncomputable abbrev Function.comp {X Y Z: Set} (g: Function Y Z) (f: Function X Y) :
    Function X Z :=
  Function.mk_fn (fun x ↦ g (f x))

infix:90 "○" => Function.comp

theorem Function.comp_eval {X Y Z: Set} (g: Function Y Z) (f: Function X Y) (x: X) :
    (g ○ f) x = g (f x) := by
  sorry

theorem Function.comp_eq_comp {X Y Z: Set} (g: Function Y Z) (f: Function X Y) :
    (g ○ f).to_fn = g.to_fn ∘ f.to_fn := by
  sorry

abbrev SetTheory.Set.f_3_3_14 : Function Nat Nat := Function.mk_fn (fun x ↦ (2*x:ℕ))

abbrev SetTheory.Set.g_3_3_14 : Function Nat Nat := Function.mk_fn (fun x ↦ (x+3:ℕ))

theorem SetTheory.Set.g_circ_f_3_3_14 :
    g_3_3_14 ○ f_3_3_14 = Function.mk_fn (fun x ↦ ((2*(x:ℕ)+3:ℕ):Nat)) := by
  sorry

theorem SetTheory.Set.f_circ_g_3_3_14 :
    f_3_3_14 ○ g_3_3_14 = Function.mk_fn (fun x ↦ ((2*(x:ℕ)+6:ℕ):Nat)) := by
  sorry

theorem SetTheory.Set.comp_assoc {W X Y Z: Set} (h: Function Y Z) (g: Function X Y)
  (f: Function W X) :
    h ○ (g ○ f) = (h ○ g) ○ f := by
  sorry

abbrev Function.one_to_one {X Y: Set} (f: Function X Y) : Prop := ∀ x x': X, x ≠ x' → f x ≠ f x'

theorem Function.one_to_one_iff {X Y: Set} (f: Function X Y) :
    f.one_to_one ↔ ∀ x x': X, f x = f x' → x = x' := by
  sorry

theorem Function.one_to_one_iff' {X Y: Set} (f: Function X Y) :
    f.one_to_one ↔ Function.Injective f.to_fn := by
  sorry

theorem SetTheory.Set.f_3_3_18_one_to_one :
    (Function.mk_fn (fun (n:Nat) ↦ ((n^2:ℕ):Nat))).one_to_one := by
  sorry

theorem SetTheory.Set.two_to_one {X Y: Set} {f: Function X Y} (h: ¬ f.one_to_one) :
    ∃ x x': X, x ≠ x' ∧ f x = f x' := by
  sorry

abbrev Function.onto {X Y: Set} (f: Function X Y) : Prop := ∀ y: Y, ∃ x: X, f x = y

theorem Function.onto_iff {X Y: Set} (f: Function X Y) : f.onto ↔ Function.Surjective f.to_fn := by
  sorry

abbrev A_3_3_21 := { m:ℤ // ∃ n:ℤ, m = n^2 }

abbrev Function.bijective {X Y: Set} (f: Function X Y) : Prop := f.one_to_one ∧ f.onto

theorem Function.bijective_iff {X Y: Set} (f: Function X Y) :
    f.bijective ↔ Function.Bijective f.to_fn := by
  sorry

abbrev f_3_3_24 : Fin 3 → ({3,4}:_root_.Set ℕ) := fun x ↦ match x with
| 0 => ⟨ 3, by norm_num ⟩
| 1 => ⟨ 3, by norm_num ⟩
| 2 => ⟨ 4, by norm_num ⟩

abbrev g_3_3_24 : Fin 2 → ({2,3,4}:_root_.Set ℕ) := fun x ↦ match x with
| 0 => ⟨ 2, by norm_num ⟩
| 1 => ⟨ 3, by norm_num ⟩

abbrev h_3_3_24 : Fin 3 → ({3,4,5}:_root_.Set ℕ) := fun x ↦ match x with
| 0 => ⟨ 3, by norm_num ⟩
| 1 => ⟨ 4, by norm_num ⟩
| 2 => ⟨ 5, by norm_num ⟩

theorem Function.bijective_incorrect_def :
    ∃ X Y: Set, ∃ f: Function X Y, (∀ x: X, ∃! y: Y, y = f x) ∧ ¬ f.bijective := by
  sorry

abbrev Function.inverse {X Y: Set} (f: Function X Y) (h: f.bijective) :
    Function Y X :=
  Function.mk (fun y x ↦ f x = y) (by
    intros
    apply existsUnique_of_exists_of_unique
    . aesop
    intro _ _ hx hx'; simp at hx hx'
    rw [←hx'] at hx
    apply f.one_to_one_iff.mp h.1
    simp [hx]
  )

theorem Function.inverse_eval {X Y: Set} {f: Function X Y} (h: f.bijective) (y: Y) (x: X) :
    x = (f.inverse h) y ↔ f x = y := by
  sorry

theorem Function.inverse_eq {X Y: Set} [Nonempty X] {f: Function X Y} (h: f.bijective) :
    (f.inverse h).to_fn = Function.invFun f.to_fn := by
  sorry
-- </CONTEXT>
-- <TARGET_THEOREM>
theorem empty_function_one_to_one_iff (X: Set) (f: Function ∅ X) : f.one_to_one ↔ sorry := by
-- </TARGET_THEOREM>

end Chapter3