Theorem: isLindelof_of_countable_subfamily_closed
File: Mathlib/Topology/Compactness/Lindelof.lean

tactic: rw [← disjoint_compl_right_iff_subset, compl_iUnion, disjoint_iff] at hsU
state_before: X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊆ ⋃ i, U i
⊢ ∃ t, t.Countable ∧ s ⊆ ⋃ i ∈ t, U i
state_after: X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊓ ⋂ i, (U i)ᶜ = ⊥
⊢ ∃ t, t.Countable ∧ s ⊆ ⋃ i ∈ t, U i

tactic: rcases h (fun i ↦ (U i)ᶜ) (fun i ↦ (hUo _).isClosed_compl) hsU with ⟨t, ht⟩
state_before: X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊓ ⋂ i, (U i)ᶜ = ⊥
⊢ ∃ t, t.Countable ∧ s ⊆ ⋃ i ∈ t, U i
state_after: case intro
X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t✝ : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊓ ⋂ i, (U i)ᶜ = ⊥
t : Set ι✝
ht : t.Countable ∧ s ∩ ⋂ i ∈ t, (U i)ᶜ = ∅
⊢ ∃ t, t.Countable ∧ s ⊆ ⋃ i ∈ t, U i

tactic: refine ⟨t, ?_⟩
state_before: case intro
X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t✝ : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊓ ⋂ i, (U i)ᶜ = ⊥
t : Set ι✝
ht : t.Countable ∧ s ∩ ⋂ i ∈ t, (U i)ᶜ = ∅
⊢ ∃ t, t.Countable ∧ s ⊆ ⋃ i ∈ t, U i
state_after: case intro
X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t✝ : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊓ ⋂ i, (U i)ᶜ = ⊥
t : Set ι✝
ht : t.Countable ∧ s ∩ ⋂ i ∈ t, (U i)ᶜ = ∅
⊢ t.Countable ∧ s ⊆ ⋃ i ∈ t, U i

tactic: rwa [← disjoint_compl_right_iff_subset, compl_iUnion₂, disjoint_iff]
state_before: case intro
X : Type u
Y : Type v
ι : Type u_1
inst✝¹ : TopologicalSpace X
inst✝ : TopologicalSpace Y
s t✝ : Set X
h :
  ∀ {ι : Type u} (t : ι → Set X),
    (∀ (i : ι), IsClosed (t i)) → s ∩ ⋂ i, t i = ∅ → ∃ u, u.Countable ∧ s ∩ ⋂ i ∈ u, t i = ∅
ι✝ : Type u
U : ι✝ → Set X
hUo : ∀ (i : ι✝), IsOpen (U i)
hsU : s ⊓ ⋂ i, (U i)ᶜ = ⊥
t : Set ι✝
ht : t.Countable ∧ s ∩ ⋂ i ∈ t, (U i)ᶜ = ∅
⊢ t.Countable ∧ s ⊆ ⋃ i ∈ t, U i
state_after: no goals