Module: Mathlib.Analysis.Normed.Group.Continuity

Goal state before:
pp: case refine_1
E : Type u_4
inst✝ : SeminormedCommGroup E
a : E
s : Subgroup E
hg : a ∈ closure[PseudoMetricSpace.toUniformSpace.toTopologicalSpace] ↑s
b : ℕ → ℝ
b_pos : ∀ (n : ℕ), 0 < b n
u : ℕ → E
u_in : ∀ (n : ℕ), u n ∈ s
lim_u : Tendsto u atTop (𝓝 a)
n₀ : ℕ
hn₀ : ∀ n ≥ n₀, ‖(u n)⁻¹ * a‖ < b 0
z : ℕ → E := fun n ↦ u (n + n₀)
lim_z : Tendsto z atTop (𝓝 a)
mem_𝓤 : ∀ (n : ℕ), {p | ‖p.1⁻¹ * p.2‖ < b (n + 1)} ∈ 𝓤 E
φ : ℕ → ℕ
φ_extr : StrictMono φ
hφ : ∀ (n : ℕ), ‖(z (φ (n + 1)))⁻¹ * z (φ n)‖ < b (n + 1)
w : ℕ → E := z ∘ φ
hw : Tendsto w atTop (𝓝 a)
v : ℕ → E := fun i ↦ if i = 0 then w 0 else (w (i - 1))⁻¹ * w i
⊢ Tendsto (fun n ↦ ∏ i ∈ range (n + 1), v i) atTop (𝓝 a)

pp: case refine_2
E : Type u_4
inst✝ : SeminormedCommGroup E
a : E
s : Subgroup E
hg : a ∈ closure[PseudoMetricSpace.toUniformSpace.toTopologicalSpace] ↑s
b : ℕ → ℝ
b_pos : ∀ (n : ℕ), 0 < b n
u : ℕ → E
u_in : ∀ (n : ℕ), u n ∈ s
lim_u : Tendsto u atTop (𝓝 a)
n₀ : ℕ
hn₀ : ∀ n ≥ n₀, ‖(u n)⁻¹ * a‖ < b 0
z : ℕ → E := fun n ↦ u (n + n₀)
lim_z : Tendsto z atTop (𝓝 a)
mem_𝓤 : ∀ (n : ℕ), {p | ‖p.1⁻¹ * p.2‖ < b (n + 1)} ∈ 𝓤 E
φ : ℕ → ℕ
φ_extr : StrictMono φ
hφ : ∀ (n : ℕ), ‖(z (φ (n + 1)))⁻¹ * z (φ n)‖ < b (n + 1)
w : ℕ → E := z ∘ φ
hw : Tendsto w atTop (𝓝 a)
v : ℕ → E := fun i ↦ if i = 0 then w 0 else (w (i - 1))⁻¹ * w i
⊢ ∀ (n : ℕ), v n ∈ s

pp: case refine_3
E : Type u_4
inst✝ : SeminormedCommGroup E
a : E
s : Subgroup E
hg : a ∈ closure[PseudoMetricSpace.toUniformSpace.toTopologicalSpace] ↑s
b : ℕ → ℝ
b_pos : ∀ (n : ℕ), 0 < b n
u : ℕ → E
u_in : ∀ (n : ℕ), u n ∈ s
lim_u : Tendsto u atTop (𝓝 a)
n₀ : ℕ
hn₀ : ∀ n ≥ n₀, ‖(u n)⁻¹ * a‖ < b 0
z : ℕ → E := fun n ↦ u (n + n₀)
lim_z : Tendsto z atTop (𝓝 a)
mem_𝓤 : ∀ (n : ℕ), {p | ‖p.1⁻¹ * p.2‖ < b (n + 1)} ∈ 𝓤 E
φ : ℕ → ℕ
φ_extr : StrictMono φ
hφ : ∀ (n : ℕ), ‖(z (φ (n + 1)))⁻¹ * z (φ n)‖ < b (n + 1)
w : ℕ → E := z ∘ φ
hw : Tendsto w atTop (𝓝 a)
v : ℕ → E := fun i ↦ if i = 0 then w 0 else (w (i - 1))⁻¹ * w i
⊢ ∀ (n : ℕ), 0 < n → ‖v n‖ < b n

Tactic:
· apply hw.congr (fun n ↦ ?_)
    rw [Finset.prod_range_succ']
    have : ∏ k ∈ range n, v (k + 1) = (v 0)⁻¹ * w n := by
      apply prod_range_induction _ _ (by simp [v]) _ (fun k hk ↦ ?_)
      simp only [↓reduceIte, Nat.add_eq_zero_iff, one_ne_zero, and_false, add_tsub_cancel_right, v]
      group
    simp [this]

Goal state after:
case refine_2
E : Type u_4
inst✝ : SeminormedCommGroup E
a : E
s : Subgroup E
hg : a ∈ closure[PseudoMetricSpace.toUniformSpace.toTopologicalSpace] ↑s
b : ℕ → ℝ
b_pos : ∀ (n : ℕ), 0 < b n
u : ℕ → E
u_in : ∀ (n : ℕ), u n ∈ s
lim_u : Tendsto u atTop (𝓝 a)
n₀ : ℕ
hn₀ : ∀ n ≥ n₀, ‖(u n)⁻¹ * a‖ < b 0
z : ℕ → E := fun n ↦ u (n + n₀)
lim_z : Tendsto z atTop (𝓝 a)
mem_𝓤 : ∀ (n : ℕ), {p | ‖p.1⁻¹ * p.2‖ < b (n + 1)} ∈ 𝓤 E
φ : ℕ → ℕ
φ_extr : StrictMono φ
hφ : ∀ (n : ℕ), ‖(z (φ (n + 1)))⁻¹ * z (φ n)‖ < b (n + 1)
w : ℕ → E := z ∘ φ
hw : Tendsto w atTop (𝓝 a)
v : ℕ → E := fun i ↦ if i = 0 then w 0 else (w (i - 1))⁻¹ * w i
⊢ ∀ (n : ℕ), v n ∈ s

case refine_3
E : Type u_4
inst✝ : SeminormedCommGroup E
a : E
s : Subgroup E
hg : a ∈ closure[PseudoMetricSpace.toUniformSpace.toTopologicalSpace] ↑s
b : ℕ → ℝ
b_pos : ∀ (n : ℕ), 0 < b n
u : ℕ → E
u_in : ∀ (n : ℕ), u n ∈ s
lim_u : Tendsto u atTop (𝓝 a)
n₀ : ℕ
hn₀ : ∀ n ≥ n₀, ‖(u n)⁻¹ * a‖ < b 0
z : ℕ → E := fun n ↦ u (n + n₀)
lim_z : Tendsto z atTop (𝓝 a)
mem_𝓤 : ∀ (n : ℕ), {p | ‖p.1⁻¹ * p.2‖ < b (n + 1)} ∈ 𝓤 E
φ : ℕ → ℕ
φ_extr : StrictMono φ
hφ : ∀ (n : ℕ), ‖(z (φ (n + 1)))⁻¹ * z (φ n)‖ < b (n + 1)
w : ℕ → E := z ∘ φ
hw : Tendsto w atTop (𝓝 a)
v : ℕ → E := fun i ↦ if i = 0 then w 0 else (w (i - 1))⁻¹ * w i
⊢ ∀ (n : ℕ), 0 < n → ‖v n‖ < b n