Theorem: subsingleton_of_disjoint_isClosed_iUnion_eq_univ
File: Mathlib/Topology/Connected/Clopen.lean

Proof steps:
state_before: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
⊢ Subsingleton ι
state_after: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i : ι
⊢ IsOpen (s i)
tactic: refine subsingleton_of_disjoint_isClopen h_nonempty h_disj (fun i ↦ ⟨h_closed i, ?_⟩)
state_before: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i : ι
⊢ IsOpen (s i)
state_after: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i : ι
⊢ IsClosed (⋃ i_1, s i_1 \ s i)
tactic: rw [← isClosed_compl_iff, compl_eq_univ_diff, ← h_Union, iUnion_diff]
state_before: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i : ι
⊢ IsClosed (⋃ i_1, s i_1 \ s i)
state_after: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i j : ι
⊢ IsClosed (s j \ s i)
tactic: refine isClosed_iUnion_of_finite (fun j ↦ ?_)
state_before: α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i j : ι
⊢ IsClosed (s j \ s i)
state_after: case inl
α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i : ι
⊢ IsClosed (s i \ s i)

case inr
α : Type u
β : Type v
ι : Type u_1
π : ι → Type u_2
inst✝² : TopologicalSpace α
s✝ t u v : Set α
inst✝¹ : PreconnectedSpace α
s : ι → Set α
h_nonempty : ∀ (i : ι), (s i).Nonempty
h_disj : Pairwise (Disjoint on s)
inst✝ : Finite ι
h_closed : ∀ (i : ι), IsClosed (s i)
h_Union : ⋃ i, s i = univ
i j : ι
h_ne : i ≠ j
⊢ IsClosed (s j \ s i)
tactic: rcases eq_or_ne i j with rfl | h_ne