-- Mathlib/Topology/Instances/ENNReal/Lemmas.lean
theorem tendsto_finset_prod_of_ne_top {ι : Type*} {f : ι → α → ℝ≥0∞} {x : Filter α} {a : ι → ℝ≥0∞}
    (s : Finset ι) (h : ∀ i ∈ s, Tendsto (f i) x (𝓝 (a i))) (h' : ∀ i ∈ s, a i ≠ ∞) :
    Tendsto (fun b => ∏ c ∈ s, f c b) x (𝓝 (∏ c ∈ s, a c))

Proof state:
case insert.ha
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ a a✝ ≠ 0 ∨ ∏ c ∈ s✝, a c ≠ ⊤

Tactic:
right

Result:
case insert.ha.h
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ ∏ c ∈ s✝, a c ≠ ⊤

Proof state:
case empty
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
h : ∀ i ∈ ∅, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ ∅, a i ≠ ⊤
⊢ Tendsto (fun b => ∏ c ∈ ∅, f c b) x (𝓝 (∏ c ∈ ∅, a c))

Tactic:
simp [tendsto_const_nhds]

Result:
no goals

Proof state:
case insert
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ Tendsto (fun b => f a✝ b * ∏ c ∈ s✝, f c b) x (𝓝 (a a✝ * ∏ c ∈ s✝, a c))

Tactic:
apply Tendsto.mul (h _ (Finset.mem_insert_self _ _))

Result:
case insert.ha
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ a a✝ ≠ 0 ∨ ∏ c ∈ s✝, a c ≠ ⊤

case insert.hmb
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ Tendsto (fun a => ∏ c ∈ s✝, f c a) x (𝓝 (∏ c ∈ s✝, a c))

case insert.hb
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ ∏ c ∈ s✝, a c ≠ 0 ∨ a a✝ ≠ ⊤

Proof state:
case insert.hmb
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ Tendsto (fun a => ∏ c ∈ s✝, f c a) x (𝓝 (∏ c ∈ s✝, a c))

Tactic:
exact IH (fun i hi => h _ (Finset.mem_insert_of_mem hi)) fun i hi =>
  h' _ (Finset.mem_insert_of_mem hi)

Result:
no goals

Proof state:
case insert.hb
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ ∏ c ∈ s✝, a c ≠ 0 ∨ a a✝ ≠ ⊤

Tactic:
exact Or.inr (h' _ (Finset.mem_insert_self _ _))

Result:
no goals

Proof state:
case insert.ha.h
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ ∏ c ∈ s✝, a c ≠ ⊤

Tactic:
exact prod_ne_top fun i hi => h' _ (Finset.mem_insert_of_mem hi)

Result:
no goals

Proof state:
case insert
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ Tendsto (fun b => ∏ c ∈ insert a✝ s✝, f c b) x (𝓝 (∏ c ∈ insert a✝ s✝, a c))

Tactic:
simp only [Finset.prod_insert has]

Result:
case insert
α : Type u_1
ι : Type u_4
f : ι → α → ℝ≥0∞
x : Filter α
a : ι → ℝ≥0∞
a✝ : ι
s✝ : Finset ι
has : a✝ ∉ s✝
IH :
  (∀ i ∈ s✝, Tendsto (f i) x (𝓝 (a i))) → (∀ i ∈ s✝, a i ≠ ⊤) → Tendsto (fun b => ∏ c ∈ s✝, f c b) x (𝓝 (∏ c ∈ s✝, a c))
h : ∀ i ∈ insert a✝ s✝, Tendsto (f i) x (𝓝 (a i))
h' : ∀ i ∈ insert a✝ s✝, a i ≠ ⊤
⊢ Tendsto (fun b => f a✝ b * ∏ c ∈ s✝, f c b) x (𝓝 (a a✝ * ∏ c ∈ s✝, a c))