l3lab/ntp-mathlib huggingface dataset:
/-- If a function `f` is differentiable in a convex open set and continuous on its closure, and its
derivative converges to a limit `f'` at a point on the boundary, then `f` is differentiable there
with derivative `f'`. -/
theorem has_fderiv_at_boundary_of_tendsto_fderiv {f : E → F} {s : Set E} {x : E} {f' : E →L[ℝ] F}
    (f_diff : DifferentiableOn ℝ f s) (s_conv : Convex ℝ s) (s_open : IsOpen s)
    (f_cont : ∀ y ∈ closure s, ContinuousWithinAt f s y)
    (h : Tendsto (fun y => fderiv ℝ f y) (𝓝[s] x) (𝓝 f')) :
    HasFDerivWithinAt f f' (closure s) x := by
  classical
    -- one can assume without loss of generality that `x` belongs to the closure of `s`, as the
    -- statement is empty otherwise
    by_cases hx : x ∉ closure s
    · rw [← closure_closure] at hx; exact hasFDerivWithinAt_of_nmem_closure hx
    push_neg at hx
    rw [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleO, Asymptotics.isLittleO_iff]
    /- One needs to show that `‖f y - f x - f' (y - x)‖ ≤ ε ‖y - x‖` for `y` close to `x` in
      `closure s`, where `ε` is an arbitrary positive constant. By continuity of the functions, it
      suffices to prove this for nearby points inside `s`. In a neighborhood of `x`, the derivative
      of `f` is arbitrarily close to `f'` by assumption. The mean value inequality completes the
      proof. -/
    intro ε ε_pos
    obtain ⟨δ, δ_pos, hδ⟩ : ∃ δ > 0, ∀ y ∈ s, dist y x < δ → ‖fderiv ℝ f y - f'‖ < ε := by
      simpa [dist_zero_right] using tendsto_nhdsWithin_nhds.1 h ε ε_pos
    set B := ball x δ
    suffices : ∀ y ∈ B ∩ closure s, ‖f y - f x - (f' y - f' x)‖ ≤ ε * ‖y - x‖
    exact mem_nhdsWithin_iff.2 ⟨δ, δ_pos, fun y hy => by simpa using this y hy⟩
    suffices
      ∀ p : E × E,
        p ∈ closure ((B ∩ s) ×ˢ (B ∩ s)) → ‖f p.2 - f p.1 - (f' p.2 - f' p.1)‖ ≤ ε * ‖p.2 - p.1‖ by
      rw [closure_prod_eq] at this
      intro y y_in
      apply this ⟨x, y⟩
      have : B ∩ closure s ⊆ closure (B ∩ s) := isOpen_ball.inter_closure
      exact ⟨this ⟨mem_ball_self δ_pos, hx⟩, this y_in⟩
    have key : ∀ p : E × E, p ∈ (B ∩ s) ×ˢ (B ∩ s) →
          ‖f p.2 - f p.1 - (f' p.2 - f' p.1)‖ ≤ ε * ‖p.2 - p.1‖ := by
      rintro ⟨u, v⟩ ⟨u_in, v_in⟩
      have conv : Convex ℝ (B ∩ s) := (convex_ball _ _).inter s_conv
      

Proof state:
case mk.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
f : E → F
s : Set E
x : E
f' : E →L[ℝ] F
f_diff : DifferentiableOn ℝ f s
s_conv : Convex ℝ s
s_open : IsOpen s
f_cont : ∀ y ∈ closure s, ContinuousWithinAt f s y
h : Tendsto (fun y => fderiv ℝ f y) (𝓝[s] x) (𝓝 f')
hx : x ∈ closure s
ε : ℝ
ε_pos : 0 < ε
δ : ℝ
δ_pos : δ > 0
hδ : ∀ y ∈ s, dist y x < δ → ‖fderiv ℝ f y - f'‖ < ε
B : Set E := ball x δ
u v : E
u_in : (u, v).1 ∈ B ∩ s
v_in : (u, v).2 ∈ B ∩ s
conv : Convex ℝ (B ∩ s)
⊢ ‖f (u, v).2 - f (u, v).1 - (f' (u, v).2 - f' (u, v).1)‖ ≤ ε * ‖(u, v).2 - (u, v).1‖

Next tactic:
have diff : DifferentiableOn ℝ f (B ∩ s) := f_diff.mono (inter_subset_right _ _)
/-- If a function `f` is differentiable in a convex open set and continuous on its closure, and its
derivative converges to a limit `f'` at a point on the boundary, then `f` is differentiable there
with derivative `f'`. -/
theorem has_fderiv_at_boundary_of_tendsto_fderiv {f : E → F} {s : Set E} {x : E} {f' : E →L[ℝ] F}
    (f_diff : DifferentiableOn ℝ f s) (s_conv : Convex ℝ s) (s_open : IsOpen s)
    (f_cont : ∀ y ∈ closure s, ContinuousWithinAt f s y)
    (h : Tendsto (fun y => fderiv ℝ f y) (𝓝[s] x) (𝓝 f')) :
    HasFDerivWithinAt f f' (closure s) x := by
  classical
    -- one can assume without loss of generality that `x` belongs to the closure of `s`, as the
    -- statement is empty otherwise
    by_cases hx : x ∉ closure s
    · rw [← closure_closure] at hx; exact hasFDerivWithinAt_of_nmem_closure hx
    push_neg at hx
    rw [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleO, Asymptotics.isLittleO_iff]
    /- One needs to show that `‖f y - f x - f' (y - x)‖ ≤ ε ‖y - x‖` for `y` close to `x` in
      `closure s`, where `ε` is an arbitrary positive constant. By continuity of the functions, it
      suffices to prove this for nearby points inside `s`. In a neighborhood of `x`, the derivative
      of `f` is arbitrarily close to `f'` by assumption. The mean value inequality completes the
      proof. -/
    intro ε ε_pos
    obtain ⟨δ, δ_pos, hδ⟩ : ∃ δ > 0, ∀ y ∈ s, dist y x < δ → ‖fderiv ℝ f y - f'‖ < ε := by
      simpa [dist_zero_right] using tendsto_nhdsWithin_nhds.1 h ε ε_pos
    set B := ball x δ
    suffices : ∀ y ∈ B ∩ closure s, ‖f y - f x - (f' y - f' x)‖ ≤ ε * ‖y - x‖
    exact mem_nhdsWithin_iff.2 ⟨δ, δ_pos, fun y hy => by simpa using this y hy⟩
    suffices
      ∀ p : E × E,
        p ∈ closure ((B ∩ s) ×ˢ (B ∩ s)) → ‖f p.2 - f p.1 - (f' p.2 - f' p.1)‖ ≤ ε * ‖p.2 - p.1‖ by
      rw [closure_prod_eq] at this
      intro y y_in
      apply this ⟨x, y⟩
      have : B ∩ closure s ⊆ closure (B ∩ s) := isOpen_ball.inter_closure
      exact ⟨this ⟨mem_ball_self δ_pos, hx⟩, this y_in⟩
    have key : ∀ p : E × E, p ∈ (B ∩ s) ×ˢ (B ∩ s) →
          ‖f p.2 - f p.1 - (f' p.2 - f' p.1)‖ ≤ ε * ‖p.2 - p.1‖ := by
      rintro ⟨u, v⟩ ⟨u_in, v_in⟩
      have conv : Convex ℝ (B ∩ s) := (convex_ball _ _).inter s_conv
      have diff : DifferentiableOn ℝ f (B ∩ s) := f_diff.mono (inter_subset_right _ _)
      have bound : ∀ z ∈ B ∩ s, ‖fderivWithin ℝ f (B ∩ s) z - f'‖ ≤ ε := by
        

Proof state:
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
f : E → F
s : Set E
x : E
f' : E →L[ℝ] F
f_diff : DifferentiableOn ℝ f s
s_conv : Convex ℝ s
s_open : IsOpen s
f_cont : ∀ y ∈ closure s, ContinuousWithinAt f s y
h : Tendsto (fun y => fderiv ℝ f y) (𝓝[s] x) (𝓝 f')
hx : x ∈ closure s
ε : ℝ
ε_pos : 0 < ε
δ : ℝ
δ_pos : δ > 0
hδ : ∀ y ∈ s, dist y x < δ → ‖fderiv ℝ f y - f'‖ < ε
B : Set E := ball x δ
u v : E
u_in : (u, v).1 ∈ B ∩ s
v_in : (u, v).2 ∈ B ∩ s
conv : Convex ℝ (B ∩ s)
diff : DifferentiableOn ℝ f (B ∩ s)
⊢ ∀ z ∈ B ∩ s, ‖fderivWithin ℝ f (B ∩ s) z - f'‖ ≤ ε

Next tactic:
intro z z_in
/-- If a function `f` is differentiable in a convex open set and continuous on its closure, and its
derivative converges to a limit `f'` at a point on the boundary, then `f` is differentiable there
with derivative `f'`. -/
theorem has_fderiv_at_boundary_of_tendsto_fderiv {f : E → F} {s : Set E} {x : E} {f' : E →L[ℝ] F}
    (f_diff : DifferentiableOn ℝ f s) (s_conv : Convex ℝ s) (s_open : IsOpen s)
    (f_cont : ∀ y ∈ closure s, ContinuousWithinAt f s y)
    (h : Tendsto (fun y => fderiv ℝ f y) (𝓝[s] x) (𝓝 f')) :
    HasFDerivWithinAt f f' (closure s) x := by
  classical
    -- one can assume without loss of generality that `x` belongs to the closure of `s`, as the
    -- statement is empty otherwise
    by_cases hx : x ∉ closure s
    · rw [← closure_closure] at hx; exact hasFDerivWithinAt_of_nmem_closure hx
    push_neg at hx
    rw [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleO, Asymptotics.isLittleO_iff]
    /- One needs to show that `‖f y - f x - f' (y - x)‖ ≤ ε ‖y - x‖` for `y` close to `x` in
      `closure s`, where `ε` is an arbitrary positive constant. By continuity of the functions, it
      suffices to prove this for nearby points inside `s`. In a neighborhood of `x`, the derivative
      of `f` is arbitrarily close to `f'` by assumption. The mean value inequality completes the
      proof. -/
    intro ε ε_pos
    obtain ⟨δ, δ_pos, hδ⟩ : ∃ δ > 0, ∀ y ∈ s, dist y x < δ → ‖fderiv ℝ f y - f'‖ < ε := by
      simpa [dist_zero_right] using tendsto_nhdsWithin_nhds.1 h ε ε_pos
    set B := ball x δ
    suffices : ∀ y ∈ B ∩ closure s, ‖f y - f x - (f' y - f' x)‖ ≤ ε * ‖y - x‖
    exact mem_nhdsWithin_iff.2 ⟨δ, δ_pos, fun y hy => by simpa using this y hy⟩
    suffices
      ∀ p : E × E,
        p ∈ closure ((B ∩ s) ×ˢ (B ∩ s)) → ‖f p.2 - f p.1 - (f' p.2 - f' p.1)‖ ≤ ε * ‖p.2 - p.1‖ by
      rw [closure_prod_eq] at this
      intro y y_in
      apply this ⟨x, y⟩
      have : B ∩ closure s ⊆ closure (B ∩ s) := isOpen_ball.inter_closure
      exact ⟨this ⟨mem_ball_self δ_pos, hx⟩, this y_in⟩
    have key : ∀ p : E × E, p ∈ (B ∩ s) ×ˢ (B ∩ s) →
          ‖f p.2 - f p.1 - (f' p.2 - f' p.1)‖ ≤ ε * ‖p.2 - p.1‖ := by
      rintro ⟨u, v⟩ ⟨u_in, v_in⟩
      have conv : Convex ℝ (B ∩ s) := (convex_ball _ _).inter s_conv
      have diff : DifferentiableOn ℝ f (B ∩ s) := f_diff.mono (inter_subset_right _ _)
      have bound : ∀ z ∈ B ∩ s, ‖fderivWithin ℝ f (B ∩ s) z - f'‖ ≤ ε := by
        intro z z_in
        

Proof state:
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
f : E → F
s : Set E
x : E
f' : E →L[ℝ] F
f_diff : DifferentiableOn ℝ f s
s_conv : Convex ℝ s
s_open : IsOpen s
f_cont : ∀ y ∈ closure s, ContinuousWithinAt f s y
h : Tendsto (fun y => fderiv ℝ f y) (𝓝[s] x) (𝓝 f')
hx : x ∈ closure s
ε : ℝ
ε_pos : 0 < ε
δ : ℝ
δ_pos : δ > 0
hδ : ∀ y ∈ s, dist y x < δ → ‖fderiv ℝ f y - f'‖ < ε
B : Set E := ball x δ
u v : E
u_in : (u, v).1 ∈ B ∩ s
v_in : (u, v).2 ∈ B ∩ s
conv : Convex ℝ (B ∩ s)
diff : DifferentiableOn ℝ f (B ∩ s)
z : E
z_in : z ∈ B ∩ s
⊢ ‖fderivWithin ℝ f (B ∩ s) z - f'‖ ≤ ε

Next tactic:
have h := hδ z
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  

Proof state:
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
let t := Ioo a b
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
ts : t ⊆ s
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
have t_diff : DifferentiableOn ℝ f t := f_diff.mono ts
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
  have t_diff : DifferentiableOn ℝ f t := f_diff.mono ts
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
ts : t ⊆ s
t_diff : DifferentiableOn ℝ f t
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
have t_conv : Convex ℝ t := convex_Ioo a b
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
  have t_diff : DifferentiableOn ℝ f t := f_diff.mono ts
  have t_conv : Convex ℝ t := convex_Ioo a b
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
ts : t ⊆ s
t_diff : DifferentiableOn ℝ f t
t_conv : Convex ℝ t
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
have t_open : IsOpen t := isOpen_Ioo
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
  have t_diff : DifferentiableOn ℝ f t := f_diff.mono ts
  have t_conv : Convex ℝ t := convex_Ioo a b
  have t_open : IsOpen t := isOpen_Ioo
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
ts : t ⊆ s
t_diff : DifferentiableOn ℝ f t
t_conv : Convex ℝ t
t_open : IsOpen t
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
have t_closure : closure t = Icc a b := closure_Ioo ab.ne
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
  have t_diff : DifferentiableOn ℝ f t := f_diff.mono ts
  have t_conv : Convex ℝ t := convex_Ioo a b
  have t_open : IsOpen t := isOpen_Ioo
  have t_closure : closure t = Icc a b := closure_Ioo ab.ne
  

Proof state:
case intro.intro
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
ts : t ⊆ s
t_diff : DifferentiableOn ℝ f t
t_conv : Convex ℝ t
t_open : IsOpen t
t_closure : closure t = Icc a b
⊢ HasDerivWithinAt f e (Ici a) a

Next tactic:
have t_cont : ∀ y ∈ closure t, ContinuousWithinAt f t y := by
    rw [t_closure]
    intro y hy
    by_cases h : y = a
    · rw [h]; exact f_lim.mono ts
    · have : y ∈ s := sab ⟨lt_of_le_of_ne hy.1 (Ne.symm h), hy.2⟩
      exact (f_diff.continuousOn y this).mono ts
/-- If a function is differentiable on the right of a point `a : ℝ`, continuous at `a`, and
its derivative also converges at `a`, then `f` is differentiable on the right at `a`. -/
theorem has_deriv_at_interval_left_endpoint_of_tendsto_deriv {s : Set ℝ} {e : E} {a : ℝ} {f : ℝ → E}
    (f_diff : DifferentiableOn ℝ f s) (f_lim : ContinuousWithinAt f s a) (hs : s ∈ 𝓝[>] a)
    (f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)) : HasDerivWithinAt f e (Ici a) a := by
  /- This is a specialization of `has_fderiv_at_boundary_of_tendsto_fderiv`. To be in the setting of
    this theorem, we need to work on an open interval with closure contained in `s ∪ {a}`, that we
    call `t = (a, b)`. Then, we check all the assumptions of this theorem and we apply it. -/
  obtain ⟨b, ab : a < b, sab : Ioc a b ⊆ s⟩ := mem_nhdsWithin_Ioi_iff_exists_Ioc_subset.1 hs
  let t := Ioo a b
  have ts : t ⊆ s := Subset.trans Ioo_subset_Ioc_self sab
  have t_diff : DifferentiableOn ℝ f t := f_diff.mono ts
  have t_conv : Convex ℝ t := convex_Ioo a b
  have t_open : IsOpen t := isOpen_Ioo
  have t_closure : closure t = Icc a b := closure_Ioo ab.ne
  have t_cont : ∀ y ∈ closure t, ContinuousWithinAt f t y := by
    

Proof state:
E : Type u_1
inst✝³ : NormedAddCommGroup E
inst✝² : NormedSpace ℝ E
F : Type u_2
inst✝¹ : NormedAddCommGroup F
inst✝ : NormedSpace ℝ F
s : Set ℝ
e : E
a : ℝ
f : ℝ → E
f_diff : DifferentiableOn ℝ f s
f_lim : ContinuousWithinAt f s a
hs : s ∈ 𝓝[>] a
f_lim' : Tendsto (fun x => deriv f x) (𝓝[>] a) (𝓝 e)
b : ℝ
ab : a < b
sab : Ioc a b ⊆ s
t : Set ℝ := Ioo a b
ts : t ⊆ s
t_diff : DifferentiableOn ℝ f t
t_conv : Convex ℝ t
t_open : IsOpen t
t_closure : closure t = Icc a b
⊢ ∀ y ∈ closure t, ContinuousWithinAt f t y

Next tactic:
rw [t_closure]