l3lab/ntp-mathlib huggingface dataset:
/-- Given any `Finset` of objects `{X, ...}` and
indexed collection of `Finset`s of morphisms `{f, ...}` in `C`,
there exists an object `S`, with a morphism `T X : S ⟶ X` from each `X`,
such that the triangles commute: `T X ≫ f = T Y`, for `f : X ⟶ Y` in the `Finset`.
-/
theorem inf_exists :
    ∃ (S : C) (T : ∀ {X : C}, X ∈ O → (S ⟶ X)),
      ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
        (⟨X, Y, mX, mY, f⟩ : Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) ∈ H →
          T mX ≫ f = T mY := by
  classical
  induction' H using Finset.induction with h' H' nmf h''
  · obtain ⟨S, f⟩ := inf_objs_exists O
    refine' ⟨S, fun mX => (f mX).some, by rintro - - - - - ⟨⟩⟩
  · obtain ⟨X, Y, mX, mY, f⟩ := h'
    obtain ⟨S', T', w'⟩ := h''
    refine' ⟨eq (T' mX ≫ f) (T' mY), fun mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ, _⟩
    intro X' Y' mX' mY' f' mf'
    rw [Category.assoc]
    by_cases h : X = X' ∧ Y = Y'
    · rcases h with ⟨rfl, rfl⟩
      by_cases hf : f = f'
      · subst hf
        apply eq_condition
      · rw [@w' _ _ mX mY f']
        simp only [Finset.mem_insert, PSigma.mk.injEq, heq_eq_eq, true_and] at mf'
        rcases mf' with mf' | mf'
        · exfalso
          exact hf mf'.symm
        · 

Proof state:
case neg.inr
C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : IsCofiltered C
O : Finset C
H H' : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
X Y : C
mX : X ∈ O
mY : Y ∈ O
f : X ⟶ Y
nmf : { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∉ H'
S' : C
T' : {X : C} → X ∈ O → (S' ⟶ X)
w' :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈ H' → T' mX ≫ f = T' mY
mX' : X ∈ O
mY' : Y ∈ O
f' : X ⟶ Y
hf : ¬f = f'
mf' : { fst := X, snd := { fst := Y, snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ∈ H'
⊢ { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f' } } } } ∈ H'

Next tactic:
exact mf'
/-- Given any `Finset` of objects `{X, ...}` and
indexed collection of `Finset`s of morphisms `{f, ...}` in `C`,
there exists an object `S`, with a morphism `T X : S ⟶ X` from each `X`,
such that the triangles commute: `T X ≫ f = T Y`, for `f : X ⟶ Y` in the `Finset`.
-/
theorem inf_exists :
    ∃ (S : C) (T : ∀ {X : C}, X ∈ O → (S ⟶ X)),
      ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
        (⟨X, Y, mX, mY, f⟩ : Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) ∈ H →
          T mX ≫ f = T mY := by
  classical
  induction' H using Finset.induction with h' H' nmf h''
  · obtain ⟨S, f⟩ := inf_objs_exists O
    refine' ⟨S, fun mX => (f mX).some, by rintro - - - - - ⟨⟩⟩
  · obtain ⟨X, Y, mX, mY, f⟩ := h'
    obtain ⟨S', T', w'⟩ := h''
    refine' ⟨eq (T' mX ≫ f) (T' mY), fun mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ, _⟩
    intro X' Y' mX' mY' f' mf'
    rw [Category.assoc]
    by_cases h : X = X' ∧ Y = Y'
    · rcases h with ⟨rfl, rfl⟩
      by_cases hf : f = f'
      · subst hf
        apply eq_condition
      · rw [@w' _ _ mX mY f']
        simp only [Finset.mem_insert, PSigma.mk.injEq, heq_eq_eq, true_and] at mf'
        rcases mf' with mf' | mf'
        · exfalso
          exact hf mf'.symm
        · exact mf'
    · 

Proof state:
case neg
C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : IsCofiltered C
O : Finset C
H H' : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
X Y : C
mX : X ∈ O
mY : Y ∈ O
f : X ⟶ Y
nmf : { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∉ H'
S' : C
T' : {X : C} → X ∈ O → (S' ⟶ X)
w' :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈ H' → T' mX ≫ f = T' mY
X' Y' : C
mX' : X' ∈ O
mY' : Y' ∈ O
f' : X' ⟶ Y'
mf' :
  { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ∈
    insert { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } H'
h : ¬(X = X' ∧ Y = Y')
⊢ eqHom (T' mX ≫ f) (T' mY) ≫ T' mX' ≫ f' = (fun {X_1} mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ) mY'

Next tactic:
rw [@w' _ _ mX' mY' f' _]
/-- Given any `Finset` of objects `{X, ...}` and
indexed collection of `Finset`s of morphisms `{f, ...}` in `C`,
there exists an object `S`, with a morphism `T X : S ⟶ X` from each `X`,
such that the triangles commute: `T X ≫ f = T Y`, for `f : X ⟶ Y` in the `Finset`.
-/
theorem inf_exists :
    ∃ (S : C) (T : ∀ {X : C}, X ∈ O → (S ⟶ X)),
      ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
        (⟨X, Y, mX, mY, f⟩ : Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) ∈ H →
          T mX ≫ f = T mY := by
  classical
  induction' H using Finset.induction with h' H' nmf h''
  · obtain ⟨S, f⟩ := inf_objs_exists O
    refine' ⟨S, fun mX => (f mX).some, by rintro - - - - - ⟨⟩⟩
  · obtain ⟨X, Y, mX, mY, f⟩ := h'
    obtain ⟨S', T', w'⟩ := h''
    refine' ⟨eq (T' mX ≫ f) (T' mY), fun mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ, _⟩
    intro X' Y' mX' mY' f' mf'
    rw [Category.assoc]
    by_cases h : X = X' ∧ Y = Y'
    · rcases h with ⟨rfl, rfl⟩
      by_cases hf : f = f'
      · subst hf
        apply eq_condition
      · rw [@w' _ _ mX mY f']
        simp only [Finset.mem_insert, PSigma.mk.injEq, heq_eq_eq, true_and] at mf'
        rcases mf' with mf' | mf'
        · exfalso
          exact hf mf'.symm
        · exact mf'
    · rw [@w' _ _ mX' mY' f' _]
      

Proof state:
C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : IsCofiltered C
O : Finset C
H H' : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
X Y : C
mX : X ∈ O
mY : Y ∈ O
f : X ⟶ Y
nmf : { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∉ H'
S' : C
T' : {X : C} → X ∈ O → (S' ⟶ X)
w' :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈ H' → T' mX ≫ f = T' mY
X' Y' : C
mX' : X' ∈ O
mY' : Y' ∈ O
f' : X' ⟶ Y'
mf' :
  { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ∈
    insert { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } H'
h : ¬(X = X' ∧ Y = Y')
⊢ { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ∈ H'

Next tactic:
apply Finset.mem_of_mem_insert_of_ne mf'
/-- Given any `Finset` of objects `{X, ...}` and
indexed collection of `Finset`s of morphisms `{f, ...}` in `C`,
there exists an object `S`, with a morphism `T X : S ⟶ X` from each `X`,
such that the triangles commute: `T X ≫ f = T Y`, for `f : X ⟶ Y` in the `Finset`.
-/
theorem inf_exists :
    ∃ (S : C) (T : ∀ {X : C}, X ∈ O → (S ⟶ X)),
      ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
        (⟨X, Y, mX, mY, f⟩ : Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) ∈ H →
          T mX ≫ f = T mY := by
  classical
  induction' H using Finset.induction with h' H' nmf h''
  · obtain ⟨S, f⟩ := inf_objs_exists O
    refine' ⟨S, fun mX => (f mX).some, by rintro - - - - - ⟨⟩⟩
  · obtain ⟨X, Y, mX, mY, f⟩ := h'
    obtain ⟨S', T', w'⟩ := h''
    refine' ⟨eq (T' mX ≫ f) (T' mY), fun mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ, _⟩
    intro X' Y' mX' mY' f' mf'
    rw [Category.assoc]
    by_cases h : X = X' ∧ Y = Y'
    · rcases h with ⟨rfl, rfl⟩
      by_cases hf : f = f'
      · subst hf
        apply eq_condition
      · rw [@w' _ _ mX mY f']
        simp only [Finset.mem_insert, PSigma.mk.injEq, heq_eq_eq, true_and] at mf'
        rcases mf' with mf' | mf'
        · exfalso
          exact hf mf'.symm
        · exact mf'
    · rw [@w' _ _ mX' mY' f' _]
      apply Finset.mem_of_mem_insert_of_ne mf'
      

Proof state:
C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : IsCofiltered C
O : Finset C
H H' : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
X Y : C
mX : X ∈ O
mY : Y ∈ O
f : X ⟶ Y
nmf : { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∉ H'
S' : C
T' : {X : C} → X ∈ O → (S' ⟶ X)
w' :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈ H' → T' mX ≫ f = T' mY
X' Y' : C
mX' : X' ∈ O
mY' : Y' ∈ O
f' : X' ⟶ Y'
mf' :
  { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ∈
    insert { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } H'
h : ¬(X = X' ∧ Y = Y')
⊢ { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ≠
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } }

Next tactic:
contrapose! h
/-- Given any `Finset` of objects `{X, ...}` and
indexed collection of `Finset`s of morphisms `{f, ...}` in `C`,
there exists an object `S`, with a morphism `T X : S ⟶ X` from each `X`,
such that the triangles commute: `T X ≫ f = T Y`, for `f : X ⟶ Y` in the `Finset`.
-/
theorem inf_exists :
    ∃ (S : C) (T : ∀ {X : C}, X ∈ O → (S ⟶ X)),
      ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
        (⟨X, Y, mX, mY, f⟩ : Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) ∈ H →
          T mX ≫ f = T mY := by
  classical
  induction' H using Finset.induction with h' H' nmf h''
  · obtain ⟨S, f⟩ := inf_objs_exists O
    refine' ⟨S, fun mX => (f mX).some, by rintro - - - - - ⟨⟩⟩
  · obtain ⟨X, Y, mX, mY, f⟩ := h'
    obtain ⟨S', T', w'⟩ := h''
    refine' ⟨eq (T' mX ≫ f) (T' mY), fun mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ, _⟩
    intro X' Y' mX' mY' f' mf'
    rw [Category.assoc]
    by_cases h : X = X' ∧ Y = Y'
    · rcases h with ⟨rfl, rfl⟩
      by_cases hf : f = f'
      · subst hf
        apply eq_condition
      · rw [@w' _ _ mX mY f']
        simp only [Finset.mem_insert, PSigma.mk.injEq, heq_eq_eq, true_and] at mf'
        rcases mf' with mf' | mf'
        · exfalso
          exact hf mf'.symm
        · exact mf'
    · rw [@w' _ _ mX' mY' f' _]
      apply Finset.mem_of_mem_insert_of_ne mf'
      contrapose! h
      

Proof state:
C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : IsCofiltered C
O : Finset C
H H' : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
X Y : C
mX : X ∈ O
mY : Y ∈ O
f : X ⟶ Y
nmf : { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∉ H'
S' : C
T' : {X : C} → X ∈ O → (S' ⟶ X)
w' :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈ H' → T' mX ≫ f = T' mY
X' Y' : C
mX' : X' ∈ O
mY' : Y' ∈ O
f' : X' ⟶ Y'
mf' :
  { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } ∈
    insert { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } H'
h :
  { fst := X', snd := { fst := Y', snd := { fst := mX', snd := { fst := mY', snd := f' } } } } =
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } }
⊢ X = X' ∧ Y = Y'

Next tactic:
obtain ⟨rfl, h⟩ := h
/-- Given any `Finset` of objects `{X, ...}` and
indexed collection of `Finset`s of morphisms `{f, ...}` in `C`,
there exists an object `S`, with a morphism `T X : S ⟶ X` from each `X`,
such that the triangles commute: `T X ≫ f = T Y`, for `f : X ⟶ Y` in the `Finset`.
-/
theorem inf_exists :
    ∃ (S : C) (T : ∀ {X : C}, X ∈ O → (S ⟶ X)),
      ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
        (⟨X, Y, mX, mY, f⟩ : Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) ∈ H →
          T mX ≫ f = T mY := by
  classical
  induction' H using Finset.induction with h' H' nmf h''
  · obtain ⟨S, f⟩ := inf_objs_exists O
    refine' ⟨S, fun mX => (f mX).some, by rintro - - - - - ⟨⟩⟩
  · obtain ⟨X, Y, mX, mY, f⟩ := h'
    obtain ⟨S', T', w'⟩ := h''
    refine' ⟨eq (T' mX ≫ f) (T' mY), fun mZ => eqHom (T' mX ≫ f) (T' mY) ≫ T' mZ, _⟩
    intro X' Y' mX' mY' f' mf'
    rw [Category.assoc]
    by_cases h : X = X' ∧ Y = Y'
    · rcases h with ⟨rfl, rfl⟩
      by_cases hf : f = f'
      · subst hf
        apply eq_condition
      · rw [@w' _ _ mX mY f']
        simp only [Finset.mem_insert, PSigma.mk.injEq, heq_eq_eq, true_and] at mf'
        rcases mf' with mf' | mf'
        · exfalso
          exact hf mf'.symm
        · exact mf'
    · rw [@w' _ _ mX' mY' f' _]
      apply Finset.mem_of_mem_insert_of_ne mf'
      contrapose! h
      obtain ⟨rfl, h⟩ := h
      

Proof state:
case refl
C : Type u
inst✝¹ : Category.{v, u} C
inst✝ : IsCofiltered C
O : Finset C
H H' : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
X Y : C
mX : X ∈ O
mY : Y ∈ O
f : X ⟶ Y
nmf : { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∉ H'
S' : C
T' : {X : C} → X ∈ O → (S' ⟶ X)
w' :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈ H' → T' mX ≫ f = T' mY
mf' :
  { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } ∈
    insert { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f } } } } H'
⊢ X = X ∧ Y = Y

Next tactic:
trivial
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O : Finset C
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
⊢ Nonempty (Cone F)

Next tactic:
classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by simp, F.map f⟩
  obtain ⟨Z, f, w⟩ := inf_exists O H
  refine' ⟨⟨Z, ⟨fun X => f (by simp), _⟩⟩⟩
  intro j j' g
  dsimp
  simp only [Category.id_comp]
  symm
  apply w
  simp only [Finset.mem_biUnion, Finset.mem_univ, Finset.mem_image,
    PSigma.mk.injEq, true_and, exists_and_left]
  exact ⟨j, rfl, j', g, by simp⟩
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O : Finset C
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
⊢ Nonempty (Cone F)

Next tactic:
let O := Finset.univ.image F.obj
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
⊢ Nonempty (Cone F)

Next tactic:
let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by simp, F.map f⟩
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by 

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
X Y : J
f : X ⟶ Y
⊢ F.obj X ∈ O

Next tactic:
simp
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by 

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
X Y : J
f : X ⟶ Y
⊢ F.obj Y ∈ O

Next tactic:
simp
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by simp, F.map f⟩
  

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H✝ : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y)) :=
  Finset.biUnion Finset.univ fun X =>
    Finset.biUnion Finset.univ fun Y =>
      Finset.image
        (fun f =>
          { fst := F.obj X,
            snd :=
              { fst := F.obj Y,
                snd :=
                  { fst := (_ : F.obj X ∈ Finset.image F.obj Finset.univ),
                    snd := { fst := (_ : F.obj Y ∈ Finset.image F.obj Finset.univ), snd := F.map f } } } })
        Finset.univ
⊢ Nonempty (Cone F)

Next tactic:
obtain ⟨Z, f, w⟩ := inf_exists O H
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by simp, F.map f⟩
  obtain ⟨Z, f, w⟩ := inf_exists O H
  

Proof state:
case intro.intro
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H✝ : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y)) :=
  Finset.biUnion Finset.univ fun X =>
    Finset.biUnion Finset.univ fun Y =>
      Finset.image
        (fun f =>
          { fst := F.obj X,
            snd :=
              { fst := F.obj Y,
                snd :=
                  { fst := (_ : F.obj X ∈ Finset.image F.obj Finset.univ),
                    snd := { fst := (_ : F.obj Y ∈ Finset.image F.obj Finset.univ), snd := F.map f } } } })
        Finset.univ
Z : C
f : {X : C} → X ∈ O → (Z ⟶ X)
w :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f_1 : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f_1 } } } } ∈ H → f mX ≫ f_1 = f mY
⊢ Nonempty (Cone F)

Next tactic:
refine' ⟨⟨Z, ⟨fun X => f (by simp), _⟩⟩⟩
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by simp, F.map f⟩
  obtain ⟨Z, f, w⟩ := inf_exists O H
  refine' ⟨⟨Z, ⟨fun X => f (by 

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H✝ : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y)) :=
  Finset.biUnion Finset.univ fun X =>
    Finset.biUnion Finset.univ fun Y =>
      Finset.image
        (fun f =>
          { fst := F.obj X,
            snd :=
              { fst := F.obj Y,
                snd :=
                  { fst := (_ : F.obj X ∈ Finset.image F.obj Finset.univ),
                    snd := { fst := (_ : F.obj Y ∈ Finset.image F.obj Finset.univ), snd := F.map f } } } })
        Finset.univ
Z : C
f : {X : C} → X ∈ O → (Z ⟶ X)
w :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f_1 : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f_1 } } } } ∈ H → f mX ≫ f_1 = f mY
X : J
⊢ F.obj X ∈ O

Next tactic:
simp
/-- If we have `IsCofiltered C`, then for any functor `F : J ⥤ C` with `FinCategory J`,
there exists a cone over `F`.
-/
theorem cone_nonempty (F : J ⥤ C) : Nonempty (Cone F) := by
  classical
  let O := Finset.univ.image F.obj
  let H : Finset (Σ' (X Y : C) (_ : X ∈ O) (_ : Y ∈ O), X ⟶ Y) :=
    Finset.univ.biUnion fun X : J =>
      Finset.univ.biUnion fun Y : J =>
        Finset.univ.image fun f : X ⟶ Y => ⟨F.obj X, F.obj Y, by simp, by simp, F.map f⟩
  obtain ⟨Z, f, w⟩ := inf_exists O H
  refine' ⟨⟨Z, ⟨fun X => f (by simp), _⟩⟩⟩
  

Proof state:
case intro.intro
C : Type u
inst✝³ : Category.{v, u} C
inst✝² : IsCofiltered C
O✝ : Finset C
H✝ : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O✝) ×' (_ : Y ∈ O✝) ×' (X ⟶ Y))
J : Type w
inst✝¹ : SmallCategory J
inst✝ : FinCategory J
F : J ⥤ C
O : Finset C := Finset.image F.obj Finset.univ
H : Finset ((X : C) ×' (Y : C) ×' (_ : X ∈ O) ×' (_ : Y ∈ O) ×' (X ⟶ Y)) :=
  Finset.biUnion Finset.univ fun X =>
    Finset.biUnion Finset.univ fun Y =>
      Finset.image
        (fun f =>
          { fst := F.obj X,
            snd :=
              { fst := F.obj Y,
                snd :=
                  { fst := (_ : F.obj X ∈ Finset.image F.obj Finset.univ),
                    snd := { fst := (_ : F.obj Y ∈ Finset.image F.obj Finset.univ), snd := F.map f } } } })
        Finset.univ
Z : C
f : {X : C} → X ∈ O → (Z ⟶ X)
w :
  ∀ {X Y : C} (mX : X ∈ O) (mY : Y ∈ O) {f_1 : X ⟶ Y},
    { fst := X, snd := { fst := Y, snd := { fst := mX, snd := { fst := mY, snd := f_1 } } } } ∈ H → f mX ≫ f_1 = f mY
⊢ ∀ ⦃X Y : J⦄ (f_1 : X ⟶ Y),
    ((Functor.const J).obj Z).map f_1 ≫ (fun X => f (_ : F.obj X ∈ Finset.image F.obj Finset.univ)) Y =
      (fun X => f (_ : F.obj X ∈ Finset.image F.obj Finset.univ)) X ≫ F.map f_1

Next tactic:
intro j j' g