-- Mathlib/Topology/StoneCech.lean
theorem ultrafilter_extend_eq_iff {f : α → γ} {b : Ultrafilter α} {c : γ} :
    Ultrafilter.extend f b = c ↔ ↑(b.map f) ≤ 𝓝 c :=
  ⟨fun h ↦ by
     -- Write b as an ultrafilter limit of pure ultrafilters, and use
     -- the facts that ultrafilter.extend is a continuous extension of f.
     let b' : Ultrafilter (Ultrafilter α) := b.map pure
     have t : ↑b' ≤ 𝓝 b := ultrafilter_converges_iff.mpr (bind_pure _).symm
     rw [← h]
     have := (continuous_ultrafilter_extend f).tendsto b
     refine le_trans ?_ (le_trans (map_mono t) this)
     change _ ≤ map (Ultrafilter.extend f ∘ pure) ↑b
     rw [ultrafilter_extend_extends]
     exact le_rfl,
   fun h ↦
    let _ : TopologicalSpace α := ⊥
    isDenseInducing_pure.extend_eq_of_tendsto
      (le_trans (map_mono (ultrafilter_comap_pure_nhds _)) h)⟩

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ map f ↑b

Tactic:
exact le_rfl

Result:
no goals

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ map (Ultrafilter.extend f ∘ pure) ↑b

Tactic:
rw [ultrafilter_extend_extends]

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ map f ↑b

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 (Ultrafilter.extend f b)

Tactic:
have := (continuous_ultrafilter_extend f).tendsto b

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 (Ultrafilter.extend f b)

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 c

Tactic:
rw [← h]

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 (Ultrafilter.extend f b)

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 c

Tactic:
let b' : Ultrafilter (Ultrafilter α) := b.map pure

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 c

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ map (Ultrafilter.extend f) ↑b'

Tactic:
change _ ≤ map (Ultrafilter.extend f ∘ pure) ↑b

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ map (Ultrafilter.extend f ∘ pure) ↑b

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 c

Tactic:
have t : ↑b' ≤ 𝓝 b := ultrafilter_converges_iff.mpr (bind_pure _).symm

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 c

Proof state:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ 𝓝 (Ultrafilter.extend f b)

Tactic:
refine le_trans ?_ (le_trans (map_mono t) this)

Result:
α : Type u
γ : Type u_1
inst✝² : TopologicalSpace γ
inst✝¹ : T2Space γ
inst✝ : CompactSpace γ
f : α → γ
b : Ultrafilter α
c : γ
h : Ultrafilter.extend f b = c
b' : Ultrafilter (Ultrafilter α) := Ultrafilter.map pure b
t : ↑b' ≤ 𝓝 b
this : Tendsto (Ultrafilter.extend f) (𝓝 b) (𝓝 (Ultrafilter.extend f b))
⊢ ↑(Ultrafilter.map f b) ≤ map (Ultrafilter.extend f) ↑b'