Module: Mathlib.Topology.Covering.Quotient

Goal state before:
pp: E : Type u_1
X : Type u_2
inst✝⁶ : TopologicalSpace E
inst✝⁵ : TopologicalSpace X
f : E → X
G : Type u_3
inst✝⁴ : Group G
inst✝³ : MulAction G E
hf : IsQuotientMap f
inst✝² : ContinuousConstSMul G E
hfG : ∀ {e₁ e₂ : E}, f e₁ = f e₂ ↔ e₁ ∈ MulAction.orbit G e₂
inst✝¹ : TopologicalSpace G
inst✝ : DiscreteTopology G
U : Set E
open_U : IsOpen[inst✝⁶] U
disjoint : ∀ (g : G), ((fun x ↦ g • x) '' U ∩ U).Nonempty → g = 1
pGE : ∀ (g : G) (e : E), f (g • e) = f e
preim_im : f ⁻¹' f '' U = ⋃ g, (fun x ↦ g • x) ⁻¹' U
this : Nonempty (X → E)
⊢ Trivialization G f

Tactic:
refine IsOpen.trivializationDiscrete (fun g ↦ (g • ·) ⁻¹' U) (f '' U)
    ?_ (fun g W hWU ↦ ⟨fun hoW ↦ (hoW.preimage hf.continuous).inter (open_U.preimage <|
      continuous_const_smul g), fun isOpen ↦ hf.isOpen_preimage.mp ?_⟩) (fun g e₁ h₁ e₂ h₂ he ↦ ?_)
    ?_ (fun {g₁ g₂} hne ↦ disjoint_iff_inf_le.mpr fun e ⟨h₁, h₂⟩ ↦ hne <|
      mul_inv_eq_one.mp (disjoint _ ⟨_, ⟨_, h₂, ?_⟩, h₁⟩)) preim_im.subset

Goal state after:
case refine_1
E : Type u_1
X : Type u_2
inst✝⁶ : TopologicalSpace E
inst✝⁵ : TopologicalSpace X
f : E → X
G : Type u_3
inst✝⁴ : Group G
inst✝³ : MulAction G E
hf : IsQuotientMap f
inst✝² : ContinuousConstSMul G E
hfG : ∀ {e₁ e₂ : E}, f e₁ = f e₂ ↔ e₁ ∈ MulAction.orbit G e₂
inst✝¹ : TopologicalSpace G
inst✝ : DiscreteTopology G
U : Set E
open_U : IsOpen[inst✝⁶] U
disjoint : ∀ (g : G), ((fun x ↦ g • x) '' U ∩ U).Nonempty → g = 1
pGE : ∀ (g : G) (e : E), f (g • e) = f e
preim_im : f ⁻¹' f '' U = ⋃ g, (fun x ↦ g • x) ⁻¹' U
this : Nonempty (X → E)
⊢ IsOpen[inst✝⁵] (f '' U)

case refine_2
E : Type u_1
X : Type u_2
inst✝⁶ : TopologicalSpace E
inst✝⁵ : TopologicalSpace X
f : E → X
G : Type u_3
inst✝⁴ : Group G
inst✝³ : MulAction G E
hf : IsQuotientMap f
inst✝² : ContinuousConstSMul G E
hfG : ∀ {e₁ e₂ : E}, f e₁ = f e₂ ↔ e₁ ∈ MulAction.orbit G e₂
inst✝¹ : TopologicalSpace G
inst✝ : DiscreteTopology G
U : Set E
open_U : IsOpen[inst✝⁶] U
disjoint : ∀ (g : G), ((fun x ↦ g • x) '' U ∩ U).Nonempty → g = 1
pGE : ∀ (g : G) (e : E), f (g • e) = f e
preim_im : f ⁻¹' f '' U = ⋃ g, (fun x ↦ g • x) ⁻¹' U
this : Nonempty (X → E)
g : G
W : Set X
hWU : W ⊆ f '' U
isOpen : IsOpen[inst✝⁶] (f ⁻¹' W ∩ (fun x ↦ g • x) ⁻¹' U)
⊢ IsOpen[inst✝⁶] (f ⁻¹' W)

case refine_3
E : Type u_1
X : Type u_2
inst✝⁶ : TopologicalSpace E
inst✝⁵ : TopologicalSpace X
f : E → X
G : Type u_3
inst✝⁴ : Group G
inst✝³ : MulAction G E
hf : IsQuotientMap f
inst✝² : ContinuousConstSMul G E
hfG : ∀ {e₁ e₂ : E}, f e₁ = f e₂ ↔ e₁ ∈ MulAction.orbit G e₂
inst✝¹ : TopologicalSpace G
inst✝ : DiscreteTopology G
U : Set E
open_U : IsOpen[inst✝⁶] U
disjoint : ∀ (g : G), ((fun x ↦ g • x) '' U ∩ U).Nonempty → g = 1
pGE : ∀ (g : G) (e : E), f (g • e) = f e
preim_im : f ⁻¹' f '' U = ⋃ g, (fun x ↦ g • x) ⁻¹' U
this : Nonempty (X → E)
g : G
e₁ : E
h₁ : e₁ ∈ (fun x ↦ g • x) ⁻¹' U
e₂ : E
h₂ : e₂ ∈ (fun x ↦ g • x) ⁻¹' U
he : f e₁ = f e₂
⊢ e₁ = e₂

case refine_4
E : Type u_1
X : Type u_2
inst✝⁶ : TopologicalSpace E
inst✝⁵ : TopologicalSpace X
f : E → X
G : Type u_3
inst✝⁴ : Group G
inst✝³ : MulAction G E
hf : IsQuotientMap f
inst✝² : ContinuousConstSMul G E
hfG : ∀ {e₁ e₂ : E}, f e₁ = f e₂ ↔ e₁ ∈ MulAction.orbit G e₂
inst✝¹ : TopologicalSpace G
inst✝ : DiscreteTopology G
U : Set E
open_U : IsOpen[inst✝⁶] U
disjoint : ∀ (g : G), ((fun x ↦ g • x) '' U ∩ U).Nonempty → g = 1
pGE : ∀ (g : G) (e : E), f (g • e) = f e
preim_im : f ⁻¹' f '' U = ⋃ g, (fun x ↦ g • x) ⁻¹' U
this : Nonempty (X → E)
⊢ ∀ (i : G), Set.SurjOn f ((fun x ↦ i • x) ⁻¹' U) (f '' U)

case refine_5
E : Type u_1
X : Type u_2
inst✝⁶ : TopologicalSpace E
inst✝⁵ : TopologicalSpace X
f : E → X
G : Type u_3
inst✝⁴ : Group G
inst✝³ : MulAction G E
hf : IsQuotientMap f
inst✝² : ContinuousConstSMul G E
hfG : ∀ {e₁ e₂ : E}, f e₁ = f e₂ ↔ e₁ ∈ MulAction.orbit G e₂
inst✝¹ : TopologicalSpace G
inst✝ : DiscreteTopology G
U : Set E
open_U : IsOpen[inst✝⁶] U
disjoint : ∀ (g : G), ((fun x ↦ g • x) '' U ∩ U).Nonempty → g = 1
pGE : ∀ (g : G) (e : E), f (g • e) = f e
preim_im : f ⁻¹' f '' U = ⋃ g, (fun x ↦ g • x) ⁻¹' U
this : Nonempty (X → E)
g₁ g₂ : G
hne : g₁ ≠ g₂
e : E
x✝ : e ∈ (fun g ↦ (fun x ↦ g • x) ⁻¹' U) g₁ ⊓ (fun g ↦ (fun x ↦ g • x) ⁻¹' U) g₂
h₁ : e ∈ (fun g ↦ (fun x ↦ g • x) ⁻¹' U) g₁
h₂ : e ∈ (fun g ↦ (fun x ↦ g • x) ⁻¹' U) g₂
⊢ (fun x ↦ (g₁ * g₂⁻¹) • x) ((fun x ↦ g₂ • x) e) = (fun x ↦ g₁ • x) e