Module: Mathlib.Topology.ShrinkingLemma

Goal state before:
pp: case refine_6
ι : Type u_1
X : Type u_2
inst✝² : TopologicalSpace X
u : ι → Set X
s : Set X
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
v : PartialRefinement u s fun w ↦ IsCompact (closure w)
hs : IsCompact s
i : ι
hi : i ∉ v.carrier
si : Set X := s ∩ (⋃ j, ⋃ (_ : j ≠ i), v.toFun j)ᶜ
hsi : si = s ∩ ⋂ i_1, ⋂ (_ : ¬i_1 = i), (v.toFun i_1)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun i
vi : Set X
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun i ∧ IsCompact (closure vi)
⊢ (fun v₁ v₂ ↦ v₁.carrier ⊆ v₂.carrier ∧ ∀ i ∈ v₁.carrier, v₁.toFun i = v₂.toFun i) v
    { toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯, closure_subset := ⋯,
      pred_of_mem := ⋯, apply_eq := ⋯ }

pp: case refine_7
ι : Type u_1
X : Type u_2
inst✝² : TopologicalSpace X
u : ι → Set X
s : Set X
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
v : PartialRefinement u s fun w ↦ IsCompact (closure w)
hs : IsCompact s
i : ι
hi : i ∉ v.carrier
si : Set X := s ∩ (⋃ j, ⋃ (_ : j ≠ i), v.toFun j)ᶜ
hsi : si = s ∩ ⋂ i_1, ⋂ (_ : ¬i_1 = i), (v.toFun i_1)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun i
vi : Set X
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun i ∧ IsCompact (closure vi)
⊢ ¬(fun v₁ v₂ ↦ v₁.carrier ⊆ v₂.carrier ∧ ∀ i ∈ v₁.carrier, v₁.toFun i = v₂.toFun i)
      { toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯,
        closure_subset := ⋯, pred_of_mem := ⋯, apply_eq := ⋯ }
      v

pp: case refine_8
ι : Type u_1
X : Type u_2
inst✝² : TopologicalSpace X
u : ι → Set X
s : Set X
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
v : PartialRefinement u s fun w ↦ IsCompact (closure w)
hs : IsCompact s
i : ι
hi : i ∉ v.carrier
si : Set X := s ∩ (⋃ j, ⋃ (_ : j ≠ i), v.toFun j)ᶜ
hsi : si = s ∩ ⋂ i_1, ⋂ (_ : ¬i_1 = i), (v.toFun i_1)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun i
vi : Set X
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun i ∧ IsCompact (closure vi)
⊢ IsCompact
    (closure
      ({ toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯,
            closure_subset := ⋯, pred_of_mem := ⋯, apply_eq := ⋯ }.toFun
        i))

Tactic:
· refine ⟨subset_insert _ _, fun j hj => ?_⟩
    exact (update_of_ne (ne_of_mem_of_not_mem hj hi) _ _).symm

Goal state after:
case refine_7
ι : Type u_1
X : Type u_2
inst✝² : TopologicalSpace X
u : ι → Set X
s : Set X
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
v : PartialRefinement u s fun w ↦ IsCompact (closure w)
hs : IsCompact s
i : ι
hi : i ∉ v.carrier
si : Set X := s ∩ (⋃ j, ⋃ (_ : j ≠ i), v.toFun j)ᶜ
hsi : si = s ∩ ⋂ i_1, ⋂ (_ : ¬i_1 = i), (v.toFun i_1)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun i
vi : Set X
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun i ∧ IsCompact (closure vi)
⊢ ¬(fun v₁ v₂ ↦ v₁.carrier ⊆ v₂.carrier ∧ ∀ i ∈ v₁.carrier, v₁.toFun i = v₂.toFun i)
      { toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯,
        closure_subset := ⋯, pred_of_mem := ⋯, apply_eq := ⋯ }
      v

case refine_8
ι : Type u_1
X : Type u_2
inst✝² : TopologicalSpace X
u : ι → Set X
s : Set X
inst✝¹ : T2Space X
inst✝ : LocallyCompactSpace X
v : PartialRefinement u s fun w ↦ IsCompact (closure w)
hs : IsCompact s
i : ι
hi : i ∉ v.carrier
si : Set X := s ∩ (⋃ j, ⋃ (_ : j ≠ i), v.toFun j)ᶜ
hsi : si = s ∩ ⋂ i_1, ⋂ (_ : ¬i_1 = i), (v.toFun i_1)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun i
vi : Set X
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun i ∧ IsCompact (closure vi)
⊢ IsCompact
    (closure
      ({ toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯,
            closure_subset := ⋯, pred_of_mem := ⋯, apply_eq := ⋯ }.toFun
        i))