Theorem: ClosedEmbedding.quasiSober
File: Mathlib/Topology/Sober.lean

Proof steps:
state_before: α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
⊢ ∃ x, IsGenericPoint x S✝
state_after: α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
⊢ ∃ x, IsGenericPoint x S✝
tactic: have hS'' := hS.image f hf.continuous.continuousOn
state_before: α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
⊢ ∃ x, IsGenericPoint x S✝
state_after: case intro
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
x : β
hx : IsGenericPoint x (f '' S✝)
⊢ ∃ x, IsGenericPoint x S✝
tactic: obtain ⟨x, hx⟩ := QuasiSober.sober hS'' (hf.isClosedMap _ hS')
state_before: case intro
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
x : β
hx : IsGenericPoint x (f '' S✝)
⊢ ∃ x, IsGenericPoint x S✝
state_after: case intro.intro.intro
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
y : α
hx : IsGenericPoint (f y) (f '' S✝)
⊢ ∃ x, IsGenericPoint x S✝
tactic: obtain ⟨y, -, rfl⟩ := hx.mem
state_before: case intro.intro.intro
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
y : α
hx : IsGenericPoint (f y) (f '' S✝)
⊢ ∃ x, IsGenericPoint x S✝
state_after: case h
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
y : α
hx : IsGenericPoint (f y) (f '' S✝)
⊢ IsGenericPoint y S✝
tactic: use y
state_before: case h
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
y : α
hx : IsGenericPoint (f y) (f '' S✝)
⊢ IsGenericPoint y S✝
state_after: case h.a
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
y : α
hx : IsGenericPoint (f y) (f '' S✝)
⊢ f '' closure {y} = f '' S✝
tactic: apply image_injective.mpr hf.inj
state_before: case h.a
α : Type u_1
β : Type u_2
inst✝² : TopologicalSpace α
inst✝¹ : TopologicalSpace β
f : α → β
hf : ClosedEmbedding f
inst✝ : QuasiSober β
S✝ : Set α
hS : IsIrreducible S✝
hS' : IsClosed S✝
hS'' : IsIrreducible (f '' S✝)
y : α
hx : IsGenericPoint (f y) (f '' S✝)
⊢ f '' closure {y} = f '' S✝
state_after: no goals
tactic: rw [← hx.def, ← hf.closure_image_eq, image_singleton]