Theorem: cardinal_eq_of_mem_nhds
File: Mathlib/Topology/Algebra/Module/Cardinality.lean

Proof steps:
state_before: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
⊢ #↑s = #E
state_after: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
⊢ #↑s = #E
tactic: let g := Homeomorph.addLeft x
state_before: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
⊢ #↑s = #E
state_after: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
⊢ #↑s = #E
tactic: let t := g ⁻¹' s
state_before: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
⊢ #↑s = #E
state_after: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
this : t ∈ 𝓝 0
⊢ #↑s = #E
tactic: have : t ∈ 𝓝 0 := g.continuous.continuousAt.preimage_mem_nhds (by simpa [g] using hs)
state_before: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
this : t ∈ 𝓝 0
⊢ #↑s = #E
state_after: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
this : t ∈ 𝓝 0
A : #↑t = #E
⊢ #↑s = #E
tactic: have A : #t = #E := cardinal_eq_of_mem_nhds_zero 𝕜 this
state_before: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
this : t ∈ 𝓝 0
A : #↑t = #E
⊢ #↑s = #E
state_after: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
this : t ∈ 𝓝 0
A : #↑t = #E
B : #↑t = #↑s
⊢ #↑s = #E
tactic: have B : #t = #s := Cardinal.mk_subtype_of_equiv s g.toEquiv
state_before: E : Type u_1
𝕜 : Type u_2
inst✝⁵ : NontriviallyNormedField 𝕜
inst✝⁴ : AddCommGroup E
inst✝³ : Module 𝕜 E
inst✝² : TopologicalSpace E
inst✝¹ : ContinuousAdd E
inst✝ : ContinuousSMul 𝕜 E
s : Set E
x : E
hs : s ∈ 𝓝 x
g : E ≃ₜ E := Homeomorph.addLeft x
t : Set E := ⇑g ⁻¹' s
this : t ∈ 𝓝 0
A : #↑t = #E
B : #↑t = #↑s
⊢ #↑s = #E
state_after: no goals
tactic: rwa [B] at A