-- Mathlib/Analysis/Normed/Algebra/Exponential.lean
theorem map_exp_of_mem_ball {F} [FunLike F 𝔸 𝔹] [RingHomClass F 𝔸 𝔹] (f : F) (hf : Continuous f)
    (x : 𝔸) (hx : x ∈ EMetric.ball (0 : 𝔸) (expSeries 𝕂 𝔸).radius) :
    f (exp 𝕂 x) = exp 𝕂 (f x)

Proof state:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ f (exp 𝕂 x) = exp 𝕂 (f x)

Tactic:
rw [exp_eq_tsum, exp_eq_tsum]

Result:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ f ((fun x => ∑' (n : ℕ), (↑n !)⁻¹ • x ^ n) x) = (fun x => ∑' (n : ℕ), (↑n !)⁻¹ • x ^ n) (f x)

Proof state:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ f ((fun x => ∑' (n : ℕ), (↑n !)⁻¹ • x ^ n) x) = (fun x => ∑' (n : ℕ), (↑n !)⁻¹ • x ^ n) (f x)

Tactic:
refine ((expSeries_summable_of_mem_ball' _ hx).hasSum.map f hf).tsum_eq.symm.trans ?_

Result:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ ∑' (b : ℕ), (⇑f ∘ fun n => (↑n !)⁻¹ • x ^ n) b = (fun x => ∑' (n : ℕ), (↑n !)⁻¹ • x ^ n) (f x)

Proof state:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ ∑' (b : ℕ), f ((↑b !)⁻¹ • x ^ b) = ∑' (n : ℕ), (↑n !)⁻¹ • f x ^ n

Tactic:
simp_rw [map_inv_natCast_smul f 𝕂 𝕂, map_pow]

Result:
no goals

Proof state:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ ∑' (b : ℕ), (⇑f ∘ fun n => (↑n !)⁻¹ • x ^ n) b = (fun x => ∑' (n : ℕ), (↑n !)⁻¹ • x ^ n) (f x)

Tactic:
dsimp only [Function.comp_def]

Result:
𝕂 : Type u_1
𝔸 : Type u_2
𝔹 : Type u_3
inst✝⁷ : NontriviallyNormedField 𝕂
inst✝⁶ : NormedRing 𝔸
inst✝⁵ : NormedRing 𝔹
inst✝⁴ : NormedAlgebra 𝕂 𝔸
inst✝³ : NormedAlgebra 𝕂 𝔹
inst✝² : CompleteSpace 𝔸
F : Type u_4
inst✝¹ : FunLike F 𝔸 𝔹
inst✝ : RingHomClass F 𝔸 𝔹
f : F
hf : Continuous ⇑f
x : 𝔸
hx : x ∈ EMetric.ball 0 (expSeries 𝕂 𝔸).radius
⊢ ∑' (b : ℕ), f ((↑b !)⁻¹ • x ^ b) = ∑' (n : ℕ), (↑n !)⁻¹ • f x ^ n