-- Mathlib/Analysis/Calculus/Taylor.lean
theorem continuousOn_taylorWithinEval {f : ℝ → E} {x : ℝ} {n : ℕ} {s : Set ℝ}
    (hs : UniqueDiffOn ℝ s) (hf : ContDiffOn ℝ n f s) :
    ContinuousOn (fun t => taylorWithinEval f n s t x) s

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
i : ℕ
hi : i ∈ Finset.range (n + 1)
⊢ ContinuousOn (iteratedDerivWithin i f s) s

Tactic:
rw [contDiffOn_nat_iff_continuousOn_differentiableOn_deriv hs] at hf

Result:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : (∀ m ≤ n, ContinuousOn (iteratedDerivWithin m f s) s) ∧ ∀ m < n, DifferentiableOn ℝ (iteratedDerivWithin m f s) s
i : ℕ
hi : i ∈ Finset.range (n + 1)
⊢ ContinuousOn (iteratedDerivWithin i f s) s

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
i : ℕ
hi : i ∈ Finset.range (n + 1)
⊢ ContinuousOn (fun t => ((↑i !)⁻¹ * (x - t) ^ i) • iteratedDerivWithin i f s t) s

Tactic:
refine (continuousOn_const.mul ((continuousOn_const.sub continuousOn_id).pow _)).smul ?_

Result:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
i : ℕ
hi : i ∈ Finset.range (n + 1)
⊢ ContinuousOn (iteratedDerivWithin i f s) s

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : (∀ m ≤ n, ContinuousOn (iteratedDerivWithin m f s) s) ∧ ∀ m < n, DifferentiableOn ℝ (iteratedDerivWithin m f s) s
i : ℕ
hi : i < n + 1
⊢ ContinuousOn (iteratedDerivWithin i f s) s

Tactic:
refine hf.1 i ?_

Result:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : (∀ m ≤ n, ContinuousOn (iteratedDerivWithin m f s) s) ∧ ∀ m < n, DifferentiableOn ℝ (iteratedDerivWithin m f s) s
i : ℕ
hi : i < n + 1
⊢ i ≤ n

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : (∀ m ≤ n, ContinuousOn (iteratedDerivWithin m f s) s) ∧ ∀ m < n, DifferentiableOn ℝ (iteratedDerivWithin m f s) s
i : ℕ
hi : i ∈ Finset.range (n + 1)
⊢ ContinuousOn (iteratedDerivWithin i f s) s

Tactic:
simp only [Finset.mem_range] at hi

Result:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : (∀ m ≤ n, ContinuousOn (iteratedDerivWithin m f s) s) ∧ ∀ m < n, DifferentiableOn ℝ (iteratedDerivWithin m f s) s
i : ℕ
hi : i < n + 1
⊢ ContinuousOn (iteratedDerivWithin i f s) s

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : (∀ m ≤ n, ContinuousOn (iteratedDerivWithin m f s) s) ∧ ∀ m < n, DifferentiableOn ℝ (iteratedDerivWithin m f s) s
i : ℕ
hi : i < n + 1
⊢ i ≤ n

Tactic:
simp only [WithTop.coe_le_coe, Nat.cast_le, Nat.lt_succ_iff.mp hi]

Result:
no goals

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
⊢ ContinuousOn (fun t => ∑ k ∈ Finset.range (n + 1), ((↑k !)⁻¹ * (x - t) ^ k) • iteratedDerivWithin k f s t) s

Tactic:
refine continuousOn_finset_sum (Finset.range (n + 1)) fun i hi => ?_

Result:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
i : ℕ
hi : i ∈ Finset.range (n + 1)
⊢ ContinuousOn (fun t => ((↑i !)⁻¹ * (x - t) ^ i) • iteratedDerivWithin i f s t) s

Proof state:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
⊢ ContinuousOn (fun t => taylorWithinEval f n s t x) s

Tactic:
simp_rw [taylor_within_apply]

Result:
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
f : ℝ → E
x : ℝ
n : ℕ
s : Set ℝ
hs : UniqueDiffOn ℝ s
hf : ContDiffOn ℝ (↑n) f s
⊢ ContinuousOn (fun t => ∑ k ∈ Finset.range (n + 1), ((↑k !)⁻¹ * (x - t) ^ k) • iteratedDerivWithin k f s t) s