Module: Mathlib.Topology.Covering.Basic

Goal state before:
pp: case inr.refine_2
E : Type u_1
X : Type u_2
inst✝² : TopologicalSpace E
inst✝¹ : TopologicalSpace X
f : E → X
inst✝ : T2Space E
x : X
hf : IsClosedMap f
fin : (f ⁻¹' {x}).Finite
h✝¹ : ∀ e ∈ f ⁻¹' {x}, ∃ φ, e ∈ φ.source ∧ ↑φ = f
this✝² : DiscreteTopology ↑(f ⁻¹' {x})
φ : ↑(f ⁻¹' {x}) → OpenPartialHomeomorph E X
hφ : ∀ (e : ↑(f ⁻¹' {x})), ↑e ∈ (φ e).source ∧ ↑(φ e) = f
V : E → Set E
hV : ∀ (x : E), x ∈ V x ∧ IsOpen[inst✝²] (V x)
disj : (f ⁻¹' {x}).PairwiseDisjoint V
V' : ↑(f ⁻¹' {x}) → Set E := fun e ↦ V ↑e ∩ (φ e).source
hV' : ∀ (e : ↑(f ⁻¹' {x})), IsOpen[inst✝²] (V' e)
this✝¹ : ⋃ e, V' e ∈ 𝓝ˢ (f ⁻¹' {x})
W : Set X
hWx : W ∈ 𝓝 x
hWV : f ⁻¹' W ⊆ ⋃ e, V' e
h✝ : Nonempty ↑(f ⁻¹' {x})
U : Set X
hUW : U ⊆ W
hU : IsOpen[inst✝¹] U
hxU : x ∈ U
U' : Set X := U ∩ ⋂ e, f '' V' e
this✝ : Finite ↑(f ⁻¹' {x})
hU' : IsOpen[inst✝¹] U'
hUV : ∀ (e : ↑(f ⁻¹' {x})), U' ⊆ f '' V' e
this : Nonempty E
e : ↑(f ⁻¹' {x})
s : Set X
hs : s ⊆ U'
h : IsOpen[inst✝²] (f ⁻¹' s ∩ V' e)
⊢ IsOpen[inst✝¹] s

pp: case inr.refine_3
E : Type u_1
X : Type u_2
inst✝² : TopologicalSpace E
inst✝¹ : TopologicalSpace X
f : E → X
inst✝ : T2Space E
x : X
hf : IsClosedMap f
fin : (f ⁻¹' {x}).Finite
h : ∀ e ∈ f ⁻¹' {x}, ∃ φ, e ∈ φ.source ∧ ↑φ = f
this✝² : DiscreteTopology ↑(f ⁻¹' {x})
φ : ↑(f ⁻¹' {x}) → OpenPartialHomeomorph E X
hφ : ∀ (e : ↑(f ⁻¹' {x})), ↑e ∈ (φ e).source ∧ ↑(φ e) = f
V : E → Set E
hV : ∀ (x : E), x ∈ V x ∧ IsOpen[inst✝²] (V x)
disj : (f ⁻¹' {x}).PairwiseDisjoint V
V' : ↑(f ⁻¹' {x}) → Set E := fun e ↦ V ↑e ∩ (φ e).source
hV' : ∀ (e : ↑(f ⁻¹' {x})), IsOpen[inst✝²] (V' e)
this✝¹ : ⋃ e, V' e ∈ 𝓝ˢ (f ⁻¹' {x})
W : Set X
hWx : W ∈ 𝓝 x
hWV : f ⁻¹' W ⊆ ⋃ e, V' e
h✝ : Nonempty ↑(f ⁻¹' {x})
U : Set X
hUW : U ⊆ W
hU : IsOpen[inst✝¹] U
hxU : x ∈ U
U' : Set X := U ∩ ⋂ e, f '' V' e
this✝ : Finite ↑(f ⁻¹' {x})
hU' : IsOpen[inst✝¹] U'
hUV : ∀ (e : ↑(f ⁻¹' {x})), U' ⊆ f '' V' e
this : Nonempty E
e : ↑(f ⁻¹' {x})
⊢ InjOn f (V' e)

Tactic:
· have : s ⊆ (φ e).target := hs.trans <| (hUV e).trans <| by
      rw [← (φ e).image_source_eq_target, (hφ e).2]; exact image_mono inter_subset_right
    rw [← (φ e).isOpen_symm_image_iff_of_subset_target this,
      (φ e).symm_image_eq_source_inter_preimage this, (hφ e).2, inter_comm]
    convert! h using 1
    refine inter_eq_inter_iff_left.mpr ⟨fun e' h ↦ h.2.2, fun e' h ↦ ⟨?_ , h.2⟩⟩
    have ⟨e'', ⟨_, mem⟩, eq⟩ := mem_iInter.mp (hs h.1).2 e
    rwa [← (φ e).injOn mem h.2 (by rwa [(hφ e).2])]

Goal state after:
case inr.refine_3
E : Type u_1
X : Type u_2
inst✝² : TopologicalSpace E
inst✝¹ : TopologicalSpace X
f : E → X
inst✝ : T2Space E
x : X
hf : IsClosedMap f
fin : (f ⁻¹' {x}).Finite
h : ∀ e ∈ f ⁻¹' {x}, ∃ φ, e ∈ φ.source ∧ ↑φ = f
this✝² : DiscreteTopology ↑(f ⁻¹' {x})
φ : ↑(f ⁻¹' {x}) → OpenPartialHomeomorph E X
hφ : ∀ (e : ↑(f ⁻¹' {x})), ↑e ∈ (φ e).source ∧ ↑(φ e) = f
V : E → Set E
hV : ∀ (x : E), x ∈ V x ∧ IsOpen[inst✝²] (V x)
disj : (f ⁻¹' {x}).PairwiseDisjoint V
V' : ↑(f ⁻¹' {x}) → Set E := fun e ↦ V ↑e ∩ (φ e).source
hV' : ∀ (e : ↑(f ⁻¹' {x})), IsOpen[inst✝²] (V' e)
this✝¹ : ⋃ e, V' e ∈ 𝓝ˢ (f ⁻¹' {x})
W : Set X
hWx : W ∈ 𝓝 x
hWV : f ⁻¹' W ⊆ ⋃ e, V' e
h✝ : Nonempty ↑(f ⁻¹' {x})
U : Set X
hUW : U ⊆ W
hU : IsOpen[inst✝¹] U
hxU : x ∈ U
U' : Set X := U ∩ ⋂ e, f '' V' e
this✝ : Finite ↑(f ⁻¹' {x})
hU' : IsOpen[inst✝¹] U'
hUV : ∀ (e : ↑(f ⁻¹' {x})), U' ⊆ f '' V' e
this : Nonempty E
e : ↑(f ⁻¹' {x})
⊢ InjOn f (V' e)