Theorem: Filter.tendsto_of_subseq_tendsto
File: Mathlib/Order/Filter/AtTopBot.lean

Proof steps:
state_before: ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ∀ (ns : ℕ → ι), Tendsto ns atTop l → ∃ ms, Tendsto (fun n => x (ns (ms n))) atTop f
⊢ Tendsto x l f
state_after: ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
⊢ ∃ ns, Tendsto ns atTop l ∧ ∀ (ms : ℕ → ℕ), ¬Tendsto (fun n => x (ns (ms n))) atTop f
tactic: contrapose! hxy
state_before: ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
⊢ ∃ ns, Tendsto ns atTop l ∧ ∀ (ms : ℕ → ℕ), ¬Tendsto (fun n => x (ns (ms n))) atTop f
state_after: case intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
⊢ ∃ ns, Tendsto ns atTop l ∧ ∀ (ms : ℕ → ℕ), ¬Tendsto (fun n => x (ns (ms n))) atTop f
tactic: obtain ⟨s, hs, hfreq⟩ : ∃ s ∈ f, ∃ᶠ n in l, x n ∉ s := by
    rwa [not_tendsto_iff_exists_frequently_nmem] at hxy
state_before: case intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
⊢ ∃ ns, Tendsto ns atTop l ∧ ∀ (ms : ℕ → ℕ), ¬Tendsto (fun n => x (ns (ms n))) atTop f
state_after: case intro.intro.intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
y : ℕ → ι
hy_tendsto : Tendsto y atTop l
hy_freq : ∀ (n : ℕ), x (y n) ∉ s
⊢ ∃ ns, Tendsto ns atTop l ∧ ∀ (ms : ℕ → ℕ), ¬Tendsto (fun n => x (ns (ms n))) atTop f
tactic: obtain ⟨y, hy_tendsto, hy_freq⟩ := exists_seq_forall_of_frequently hfreq
state_before: case intro.intro.intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
y : ℕ → ι
hy_tendsto : Tendsto y atTop l
hy_freq : ∀ (n : ℕ), x (y n) ∉ s
⊢ ∃ ns, Tendsto ns atTop l ∧ ∀ (ms : ℕ → ℕ), ¬Tendsto (fun n => x (ns (ms n))) atTop f
state_after: case intro.intro.intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
y : ℕ → ι
hy_tendsto : Tendsto y atTop l
hy_freq : ∀ (n : ℕ), x (y n) ∉ s
ms : ℕ → ℕ
hms_tendsto : Tendsto (fun n => x (y (ms n))) atTop f
⊢ False
tactic: refine ⟨y, hy_tendsto, fun ms hms_tendsto ↦ ?_⟩
state_before: case intro.intro.intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
y : ℕ → ι
hy_tendsto : Tendsto y atTop l
hy_freq : ∀ (n : ℕ), x (y n) ∉ s
ms : ℕ → ℕ
hms_tendsto : Tendsto (fun n => x (y (ms n))) atTop f
⊢ False
state_after: case intro.intro.intro.intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
y : ℕ → ι
hy_tendsto : Tendsto y atTop l
hy_freq : ∀ (n : ℕ), x (y n) ∉ s
ms : ℕ → ℕ
hms_tendsto : Tendsto (fun n => x (y (ms n))) atTop f
n : ℕ
hn : x (y (ms n)) ∈ s
⊢ False
tactic: rcases (hms_tendsto.eventually_mem hs).exists with ⟨n, hn⟩
state_before: case intro.intro.intro.intro.intro
ι✝ : Type u_1
ι' : Type u_2
α : Type u_3
β : Type u_4
γ : Type u_5
ι : Type u_6
x : ι → α
f : Filter α
l : Filter ι
inst✝ : l.IsCountablyGenerated
hxy : ¬Tendsto x l f
s : Set α
hs : s ∈ f
hfreq : ∃ᶠ (n : ι) in l, x n ∉ s
y : ℕ → ι
hy_tendsto : Tendsto y atTop l
hy_freq : ∀ (n : ℕ), x (y n) ∉ s
ms : ℕ → ℕ
hms_tendsto : Tendsto (fun n => x (y (ms n))) atTop f
n : ℕ
hn : x (y (ms n)) ∈ s
⊢ False
state_after: no goals
tactic: exact absurd hn <| hy_freq _