Theorem: PartitionOfUnity.exists_finset_nhd'
File: Mathlib/Topology/PartitionOfUnity.lean

Proof steps:
state_before: ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
⊢ ∃ I, (∀ᶠ (x : X) in 𝓝[s] x₀, ∑ i ∈ I, (ρ i) x = 1) ∧ ∀ᶠ (x : X) in 𝓝 x₀, (support fun x_1 => (ρ x_1) x) ⊆ ↑I
state_after: case intro
ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
I : Finset ι
hI : ∀ᶠ (x : X) in 𝓝 x₀, (support fun i => (ρ i) x) ⊆ ↑I
⊢ ∃ I, (∀ᶠ (x : X) in 𝓝[s] x₀, ∑ i ∈ I, (ρ i) x = 1) ∧ ∀ᶠ (x : X) in 𝓝 x₀, (support fun x_1 => (ρ x_1) x) ⊆ ↑I
tactic: rcases ρ.locallyFinite.exists_finset_support x₀ with ⟨I, hI⟩
state_before: case intro
ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
I : Finset ι
hI : ∀ᶠ (x : X) in 𝓝 x₀, (support fun i => (ρ i) x) ⊆ ↑I
⊢ ∃ I, (∀ᶠ (x : X) in 𝓝[s] x₀, ∑ i ∈ I, (ρ i) x = 1) ∧ ∀ᶠ (x : X) in 𝓝 x₀, (support fun x_1 => (ρ x_1) x) ⊆ ↑I
state_after: case intro
ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
I : Finset ι
hI : ∀ᶠ (x : X) in 𝓝 x₀, (support fun i => (ρ i) x) ⊆ ↑I
x : X
hx : (support fun i => (ρ i) x) ⊆ ↑I
x_in : x ∈ s
⊢ ∑ i ∈ I, (ρ i) x = 1
tactic: refine ⟨I, eventually_nhdsWithin_iff.mpr (hI.mono fun x hx x_in ↦ ?_), hI⟩
state_before: case intro
ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
I : Finset ι
hI : ∀ᶠ (x : X) in 𝓝 x₀, (support fun i => (ρ i) x) ⊆ ↑I
x : X
hx : (support fun i => (ρ i) x) ⊆ ↑I
x_in : x ∈ s
⊢ ∑ i ∈ I, (ρ i) x = 1
state_after: case intro
ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
I : Finset ι
hI : ∀ᶠ (x : X) in 𝓝 x₀, (support fun i => (ρ i) x) ⊆ ↑I
x : X
hx : (support fun i => (ρ i) x) ⊆ ↑I
x_in : x ∈ s
this : ∑ᶠ (i : ι), (ρ i) x = ∑ i ∈ I, (ρ i) x
⊢ ∑ i ∈ I, (ρ i) x = 1
tactic: have : ∑ᶠ i : ι, ρ i x = ∑ i ∈ I, ρ i x := finsum_eq_sum_of_support_subset _ hx
state_before: case intro
ι : Type u
X : Type v
inst✝⁴ : TopologicalSpace X
E : Type u_1
inst✝³ : AddCommMonoid E
inst✝² : SMulWithZero ℝ E
inst✝¹ : TopologicalSpace E
inst✝ : ContinuousSMul ℝ E
s✝ : Set X
f : PartitionOfUnity ι X s✝
s : Set X
ρ : PartitionOfUnity ι X s
x₀ : X
I : Finset ι
hI : ∀ᶠ (x : X) in 𝓝 x₀, (support fun i => (ρ i) x) ⊆ ↑I
x : X
hx : (support fun i => (ρ i) x) ⊆ ↑I
x_in : x ∈ s
this : ∑ᶠ (i : ι), (ρ i) x = ∑ i ∈ I, (ρ i) x
⊢ ∑ i ∈ I, (ρ i) x = 1
state_after: no goals
tactic: rwa [eq_comm, ρ.sum_eq_one x_in] at this