Theorem: TopologicalGroup.exists_antitone_basis_nhds_one
File: Mathlib/Topology/Algebra/Group/Basic.lean

Proof steps:
state_before: G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
state_after: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
tactic: rcases (𝓝 (1 : G)).exists_antitone_basis with ⟨u, hu, u_anti⟩
state_before: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
state_after: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), True → ∃ ia, (True ∧ True) ∧ ∀ x ∈ u ia.1 ×ˢ u ia.2, x.1 * x.2 ∈ u ib
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
tactic: have :=
    ((hu.prod_nhds hu).tendsto_iff hu).mp
      (by simpa only [mul_one] using continuous_mul.tendsto ((1, 1) : G × G))
state_before: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), True → ∃ ia, (True ∧ True) ∧ ∀ x ∈ u ia.1 ×ˢ u ia.2, x.1 * x.2 ∈ u ib
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
state_after: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), ∃ a b, True ∧ ∀ (a_1 b_1 : G), a_1 ∈ u a → b_1 ∈ u b → a_1 * b_1 ∈ u ib
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
tactic: simp only [and_self_iff, mem_prod, and_imp, Prod.forall, exists_true_left, Prod.exists,
    forall_true_left] at this
state_before: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), ∃ a b, True ∧ ∀ (a_1 b_1 : G), a_1 ∈ u a → b_1 ∈ u b → a_1 * b_1 ∈ u ib
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
state_after: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), ∃ a b, True ∧ ∀ (a_1 b_1 : G), a_1 ∈ u a → b_1 ∈ u b → a_1 * b_1 ∈ u ib
event_mul : ∀ (n : ℕ), ∀ᶠ (m : ℕ) in atTop, u m * u m ⊆ u n
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
tactic: have event_mul : ∀ n : ℕ, ∀ᶠ m in atTop, u m * u m ⊆ u n := by
    intro n
    rcases this n with ⟨j, k, -, h⟩
    refine atTop_basis.eventually_iff.mpr ⟨max j k, True.intro, fun m hm => ?_⟩
    rintro - ⟨a, ha, b, hb, rfl⟩
    exact h a b (u_anti ((le_max_left _ _).trans hm) ha) (u_anti ((le_max_right _ _).trans hm) hb)
state_before: case intro.mk
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), ∃ a b, True ∧ ∀ (a_1 b_1 : G), a_1 ∈ u a → b_1 ∈ u b → a_1 * b_1 ∈ u ib
event_mul : ∀ (n : ℕ), ∀ᶠ (m : ℕ) in atTop, u m * u m ⊆ u n
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
state_after: case intro.mk.intro.intro.intro
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), ∃ a b, True ∧ ∀ (a_1 b_1 : G), a_1 ∈ u a → b_1 ∈ u b → a_1 * b_1 ∈ u ib
event_mul : ∀ (n : ℕ), ∀ᶠ (m : ℕ) in atTop, u m * u m ⊆ u n
φ : ℕ → ℕ
hφ : ∀ ⦃m n : ℕ⦄, m < n → u (φ n) * u (φ n) ⊆ u (φ m)
φ_anti_basis : (𝓝 1).HasAntitoneBasis (u ∘ φ)
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
tactic: obtain ⟨φ, -, hφ, φ_anti_basis⟩ := HasAntitoneBasis.subbasis_with_rel ⟨hu, u_anti⟩ event_mul
state_before: case intro.mk.intro.intro.intro
G : Type w
H : Type x
α : Type u
β : Type v
inst✝³ : TopologicalSpace G
inst✝² : Group G
inst✝¹ : TopologicalGroup G
N : Subgroup G
n : N.Normal
inst✝ : FirstCountableTopology G
u : ℕ → Set G
hu : (𝓝 1).HasBasis (fun x => True) u
u_anti : Antitone u
this : ∀ (ib : ℕ), ∃ a b, True ∧ ∀ (a_1 b_1 : G), a_1 ∈ u a → b_1 ∈ u b → a_1 * b_1 ∈ u ib
event_mul : ∀ (n : ℕ), ∀ᶠ (m : ℕ) in atTop, u m * u m ⊆ u n
φ : ℕ → ℕ
hφ : ∀ ⦃m n : ℕ⦄, m < n → u (φ n) * u (φ n) ⊆ u (φ m)
φ_anti_basis : (𝓝 1).HasAntitoneBasis (u ∘ φ)
⊢ ∃ u, (𝓝 1).HasAntitoneBasis u ∧ ∀ (n : ℕ), u (n + 1) * u (n + 1) ⊆ u n
state_after: no goals
tactic: exact ⟨u ∘ φ, φ_anti_basis, fun n => hφ n.lt_succ_self⟩