-- Mathlib/Topology/Algebra/Group/OpenMapping.lean
theorem smul_singleton_mem_nhds_of_sigmaCompact
    {U : Set G} (hU : U ∈ 𝓝 1) (x : X) : U • {x} ∈ 𝓝 x

Proof state:
case hc.mk.mk.hs.hs
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
this✝ : Nonempty X
this : Encodable ↑s
n : ℕ
g : G
hg : g ∈ s
⊢ IsCompact (K n ∩ g • V)

Tactic:
exact (isCompact_compactCovering G n).inter_right (V_closed.smul g)

Result:
no goals

Proof state:
case hc
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
this✝ : Nonempty X
this : Encodable ↑s
⊢ ∀ (i : ℕ × ↑s), IsClosed (F i)

Tactic:
rintro ⟨n, ⟨g, hg⟩⟩

Result:
case hc.mk.mk
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
this✝ : Nonempty X
this : Encodable ↑s
n : ℕ
g : G
hg : g ∈ s
⊢ IsClosed (F (n, ⟨g, hg⟩))

Proof state:
case hc.mk.mk.hs.hf
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
this✝ : Nonempty X
this : Encodable ↑s
n : ℕ
g : G
hg : g ∈ s
⊢ Continuous fun g => g • x

Tactic:
exact continuous_id.smul continuous_const

Result:
no goals

Proof state:
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
⊢ ∃ i, (interior (F i)).Nonempty

Tactic:
have : Nonempty X := ⟨x⟩

Result:
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
this : Nonempty X
⊢ ∃ i, (interior (F i)).Nonempty

Proof state:
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
n : ℕ
g : G
hg : g ∈ s
hi : (interior (F (n, ⟨g, hg⟩))).Nonempty
I : (interior ((g • V) • {x})).Nonempty
g' : G
hg' : g' ∈ V
hy : g' • x ∈ interior (V • {x})
J : (g'⁻¹ • V) • {x} ∈ 𝓝 x
⊢ (g'⁻¹ • V) • {x} ⊆ U • {x}

Tactic:
apply smul_subset_smul_right

Result:
case a
G : Type u_1
X : Type u_2
inst✝⁹ : TopologicalSpace G
inst✝⁸ : TopologicalSpace X
inst✝⁷ : Group G
inst✝⁶ : IsTopologicalGroup G
inst✝⁵ : MulAction G X
inst✝⁴ : SigmaCompactSpace G
inst✝³ : BaireSpace X
inst✝² : T2Space X
inst✝¹ : ContinuousSMul G X
inst✝ : IsPretransitive G X
U : Set G
hU : U ∈ 𝓝 1
x : X
V : Set G
V_mem : V ∈ 𝓝 1
V_closed : IsClosed V
V_symm : V⁻¹ = V
VU : V * V ⊆ U
s : Set G
s_count : s.Countable
hs : ⋃ g ∈ s, g • V = univ
K : ℕ → Set G := compactCovering G
F : ℕ × ↑s → Set X := fun p => (K p.1 ∩ ↑p.2 • V) • {x}
n : ℕ
g : G
hg : g ∈ s
hi : (interior (F (n, ⟨g, hg⟩))).Nonempty
I : (interior ((g • V) • {x})).Nonempty
g' : G
hg' : g' ∈ V
hy : g' • x ∈ interior (V • {x})
J : (g'⁻¹ • V) • {x} ∈ 𝓝 x
⊢ g'⁻¹ • V ⊆ U