Theorem: IsCompact.binary_compact_cover
File: Mathlib/Topology/Separation.lean

Proof steps:
state_before: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
state_after: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
tactic: have hK' : IsCompact (closure K) := hK.closure
state_before: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
state_after: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
this : SeparatedNhds (closure K \ U) (closure K \ V)
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
tactic: have : SeparatedNhds (closure K \ U) (closure K \ V) := by
    apply SeparatedNhds.of_isCompact_isCompact_isClosed (hK'.diff hU) (hK'.diff hV)
      (isClosed_closure.sdiff hV)
    rw [disjoint_iff_inter_eq_empty, diff_inter_diff, diff_eq_empty]
    exact hK.closure_subset_of_isOpen (hU.union hV) h2K
state_before: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
this : SeparatedNhds (closure K \ U) (closure K \ V)
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
state_after: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
this✝ : SeparatedNhds (closure K \ U) (closure K \ V)
this : SeparatedNhds (K \ U) (K \ V)
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
tactic: have : SeparatedNhds (K \ U) (K \ V) :=
    this.mono (diff_subset_diff_left (subset_closure)) (diff_subset_diff_left (subset_closure))
state_before: X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
this✝ : SeparatedNhds (closure K \ U) (closure K \ V)
this : SeparatedNhds (K \ U) (K \ V)
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
state_after: case intro.intro.intro.intro.intro.intro
X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
this : SeparatedNhds (closure K \ U) (closure K \ V)
O₁ O₂ : Set X
h1O₁ : IsOpen O₁
h1O₂ : IsOpen O₂
h2O₁ : K \ U ⊆ O₁
h2O₂ : K \ V ⊆ O₂
hO : Disjoint O₁ O₂
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
tactic: rcases this with ⟨O₁, O₂, h1O₁, h1O₂, h2O₁, h2O₂, hO⟩
state_before: case intro.intro.intro.intro.intro.intro
X : Type u_1
Y : Type u_2
inst✝² : TopologicalSpace X
inst✝¹ : FirstCountableTopology X
inst✝ : R1Space X
x y : X
K U V : Set X
hK : IsCompact K
hU : IsOpen U
hV : IsOpen V
h2K : K ⊆ U ∪ V
hK' : IsCompact (closure K)
this : SeparatedNhds (closure K \ U) (closure K \ V)
O₁ O₂ : Set X
h1O₁ : IsOpen O₁
h1O₂ : IsOpen O₂
h2O₁ : K \ U ⊆ O₁
h2O₂ : K \ V ⊆ O₂
hO : Disjoint O₁ O₂
⊢ ∃ K₁ K₂, IsCompact K₁ ∧ IsCompact K₂ ∧ K₁ ⊆ U ∧ K₂ ⊆ V ∧ K = K₁ ∪ K₂
state_after: no goals
tactic: exact ⟨K \ O₁, K \ O₂, hK.diff h1O₁, hK.diff h1O₂, diff_subset_comm.mp h2O₁,
    diff_subset_comm.mp h2O₂, by rw [← diff_inter, hO.inter_eq, diff_empty]⟩