-- Mathlib/Topology/ShrinkingLemma.lean
theorem exists_gt_t2space (v : PartialRefinement u s (fun w => IsCompact (closure w)))
    (hs : IsCompact s) (i : ι) (hi : i ∉ v.carrier) :
    ∃ v' : PartialRefinement u s (fun w => IsCompact (closure w)),
      v < v' ∧ IsCompact (closure (v' i))

Proof state:
case intro.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)
⊢ v.carrier ⊆
      { toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯,
          closure_subset := ⋯, pred_of_mem := ⋯, apply_eq := ⋯ }.carrier ∧
    ∀ i_1 ∈ v.carrier,
      v.toFun i_1 =
        { toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯,
              closure_subset := ⋯, pred_of_mem := ⋯, apply_eq := ⋯ }.toFun
          i_1

Tactic:
refine ⟨subset_insert _ _, fun j hj => ?_⟩

Result:
case intro.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)
j : ι
hj : j ∈ v.carrier
⊢ v.toFun j =
    { toFun := update v.toFun i vi, carrier := insert i v.carrier, isOpen := ⋯, subset_iUnion := ⋯, closure_subset := ⋯,
          pred_of_mem := ⋯, apply_eq := ⋯ }.toFun
      j

Proof state:
case neg.left
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)
j : ι
hj : j = i ∨ j ∈ v.carrier
h : ¬j = i
hji : j = i
⊢ IsCompact (closure (update v.toFun i vi j))

Tactic:
exact False.elim (h hji)

Result:
no goals

Proof state:
case intro.refine_3.inl
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
vi : Set X
j : ι
hi : j ∉ v.carrier
si : Set X := s ∩ (⋃ j_1, ⋃ (_ : j_1 ≠ j), v.toFun j_1)ᶜ
hsi : si = s ∩ ⋂ i, ⋂ (_ : ¬i = j), (v.toFun i)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun j
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun j ∧ IsCompact (closure vi)
⊢ closure vi ⊆ u j

Tactic:
exact subset_trans hvi.2.2.1 <| PartialRefinement.subset v j

Result:
no goals

Proof state:
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 ∩ (⋃ j, ⋃ (_ : j ≠ i), v.toFun j)ᶜ
⊢ ∃ v', v < v' ∧ IsCompact (closure (v'.toFun i))

Tactic:
simp only [ne_eq, compl_iUnion] at hsi

Result:
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
⊢ ∃ v', v < v' ∧ IsCompact (closure (v'.toFun i))

Proof state:
case intro.refine_3.inl
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
vi : Set X
j : ι
hi : j ∉ v.carrier
si : Set X := s ∩ (⋃ j_1, ⋃ (_ : j_1 ≠ j), v.toFun j_1)ᶜ
hsi : si = s ∩ ⋂ i, ⋂ (_ : ¬i = j), (v.toFun i)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun j
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun j ∧ IsCompact (closure vi)
⊢ closure (update v.toFun j vi j) ⊆ u j

Tactic:
rw [update_self]

Result:
case intro.refine_3.inl
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
vi : Set X
j : ι
hi : j ∉ v.carrier
si : Set X := s ∩ (⋃ j_1, ⋃ (_ : j_1 ≠ j), v.toFun j_1)ᶜ
hsi : si = s ∩ ⋂ i, ⋂ (_ : ¬i = j), (v.toFun i)ᶜ
hsic : IsCompact si
this : si ⊆ v.toFun j
hvi : IsOpen vi ∧ si ⊆ vi ∧ closure vi ⊆ v.toFun j ∧ IsCompact (closure vi)
⊢ closure vi ⊆ u j

Proof state:
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
x : X
hx : x ∈ si
this : ∀ (j : ι), j ≠ i → x ∉ v.toFun j
j : ι
hj : x ∈ v.toFun j
⊢ j = i

Tactic:
by_contra! h

Result:
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
x : X
hx : x ∈ si
this : ∀ (j : ι), j ≠ i → x ∉ v.toFun j
j : ι
hj : x ∈ v.toFun j
h : j ≠ i
⊢ False

Proof state:
case intro.refine_1
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)
⊢ ∀ (i_1 : ι), IsOpen (update v.toFun i vi i_1)

Tactic:
intro j

Result:
case intro.refine_1
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)
j : ι
⊢ IsOpen (update v.toFun i vi j)