l3lab/ntp-mathlib huggingface dataset:
/-- If `f` is a continuous monotone map `ℝ → ℝ`, `f (x + 1) = f x + 1`, then there exists `x`
such that `f x = x + τ f`. -/
theorem exists_eq_add_translationNumber (hf : Continuous f) : ∃ x, f x = x + τ f := by
  obtain ⟨a, ha⟩ : ∃ x, f x ≤ x + τ f := by
    by_contra! H
    exact lt_irrefl _ (f.lt_translationNumber_of_forall_add_lt hf H)
  

Proof state:
case intro
f g : CircleDeg1Lift
hf : Continuous ⇑f
a : ℝ
ha : f a ≤ a + τ f
⊢ ∃ x, f x = x + τ f

Next tactic:
obtain ⟨b, hb⟩ : ∃ x, x + τ f ≤ f x := by
    by_contra! H
    exact lt_irrefl _ (f.translationNumber_lt_of_forall_lt_add hf H)
/-- If `f` is a continuous monotone map `ℝ → ℝ`, `f (x + 1) = f x + 1`, then there exists `x`
such that `f x = x + τ f`. -/
theorem exists_eq_add_translationNumber (hf : Continuous f) : ∃ x, f x = x + τ f := by
  obtain ⟨a, ha⟩ : ∃ x, f x ≤ x + τ f := by
    by_contra! H
    exact lt_irrefl _ (f.lt_translationNumber_of_forall_add_lt hf H)
  obtain ⟨b, hb⟩ : ∃ x, x + τ f ≤ f x := by
    

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
a : ℝ
ha : f a ≤ a + τ f
⊢ ∃ x, x + τ f ≤ f x

Next tactic:
by_contra! H
/-- If `f` is a continuous monotone map `ℝ → ℝ`, `f (x + 1) = f x + 1`, then there exists `x`
such that `f x = x + τ f`. -/
theorem exists_eq_add_translationNumber (hf : Continuous f) : ∃ x, f x = x + τ f := by
  obtain ⟨a, ha⟩ : ∃ x, f x ≤ x + τ f := by
    by_contra! H
    exact lt_irrefl _ (f.lt_translationNumber_of_forall_add_lt hf H)
  obtain ⟨b, hb⟩ : ∃ x, x + τ f ≤ f x := by
    by_contra! H
    

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
a : ℝ
ha : f a ≤ a + τ f
H : ∀ (x : ℝ), f x < x + τ f
⊢ False

Next tactic:
exact lt_irrefl _ (f.translationNumber_lt_of_forall_lt_add hf H)
/-- If `f` is a continuous monotone map `ℝ → ℝ`, `f (x + 1) = f x + 1`, then there exists `x`
such that `f x = x + τ f`. -/
theorem exists_eq_add_translationNumber (hf : Continuous f) : ∃ x, f x = x + τ f := by
  obtain ⟨a, ha⟩ : ∃ x, f x ≤ x + τ f := by
    by_contra! H
    exact lt_irrefl _ (f.lt_translationNumber_of_forall_add_lt hf H)
  obtain ⟨b, hb⟩ : ∃ x, x + τ f ≤ f x := by
    by_contra! H
    exact lt_irrefl _ (f.translationNumber_lt_of_forall_lt_add hf H)
  

Proof state:
case intro.intro
f g : CircleDeg1Lift
hf : Continuous ⇑f
a : ℝ
ha : f a ≤ a + τ f
b : ℝ
hb : b + τ f ≤ f b
⊢ ∃ x, f x = x + τ f

Next tactic:
exact intermediate_value_univ₂ hf (continuous_id.add continuous_const) ha hb
theorem translationNumber_eq_int_iff (hf : Continuous f) {m : ℤ} :
    τ f = m ↔ ∃ x : ℝ, f x = x + m := by
  

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
⊢ τ f = ↑m ↔ ∃ x, f x = x + ↑m

Next tactic:
constructor
theorem translationNumber_eq_int_iff (hf : Continuous f) {m : ℤ} :
    τ f = m ↔ ∃ x : ℝ, f x = x + m := by
  constructor
  · 

Proof state:
case mp
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
⊢ τ f = ↑m → ∃ x, f x = x + ↑m

Next tactic:
intro h
theorem translationNumber_eq_int_iff (hf : Continuous f) {m : ℤ} :
    τ f = m ↔ ∃ x : ℝ, f x = x + m := by
  constructor
  · intro h
    

Proof state:
case mp
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
h : τ f = ↑m
⊢ ∃ x, f x = x + ↑m

Next tactic:
simp only [← h]
theorem translationNumber_eq_int_iff (hf : Continuous f) {m : ℤ} :
    τ f = m ↔ ∃ x : ℝ, f x = x + m := by
  constructor
  · intro h
    simp only [← h]
    

Proof state:
case mp
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
h : τ f = ↑m
⊢ ∃ x, f x = x + τ f

Next tactic:
exact f.exists_eq_add_translationNumber hf
theorem translationNumber_eq_int_iff (hf : Continuous f) {m : ℤ} :
    τ f = m ↔ ∃ x : ℝ, f x = x + m := by
  constructor
  · intro h
    simp only [← h]
    exact f.exists_eq_add_translationNumber hf
  · 

Proof state:
case mpr
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
⊢ (∃ x, f x = x + ↑m) → τ f = ↑m

Next tactic:
rintro ⟨x, hx⟩
theorem translationNumber_eq_int_iff (hf : Continuous f) {m : ℤ} :
    τ f = m ↔ ∃ x : ℝ, f x = x + m := by
  constructor
  · intro h
    simp only [← h]
    exact f.exists_eq_add_translationNumber hf
  · rintro ⟨x, hx⟩
    

Proof state:
case mpr.intro
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
x : ℝ
hx : f x = x + ↑m
⊢ τ f = ↑m

Next tactic:
exact f.translationNumber_of_eq_add_int hx
theorem continuous_pow (hf : Continuous f) (n : ℕ) : Continuous (f ^ n : CircleDeg1Lift) := by
  

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
n : ℕ
⊢ Continuous ⇑(f ^ n)

Next tactic:
rw [coe_pow]
theorem continuous_pow (hf : Continuous f) (n : ℕ) : Continuous (f ^ n : CircleDeg1Lift) := by
  rw [coe_pow]
  

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
n : ℕ
⊢ Continuous (⇑f)^[n]

Next tactic:
exact hf.iterate n
theorem translationNumber_eq_rat_iff (hf : Continuous f) {m : ℤ} {n : ℕ} (hn : 0 < n) :
    τ f = m / n ↔ ∃ x, (f ^ n) x = x + m := by
  

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
n : ℕ
hn : 0 < n
⊢ τ f = ↑m / ↑n ↔ ∃ x, (f ^ n) x = x + ↑m

Next tactic:
rw [eq_div_iff, mul_comm, ← translationNumber_pow] <;> [skip; exact ne_of_gt (Nat.cast_pos.2 hn)]
theorem translationNumber_eq_rat_iff (hf : Continuous f) {m : ℤ} {n : ℕ} (hn : 0 < n) :
    τ f = m / n ↔ ∃ x, (f ^ n) x = x + m := by
  

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
n : ℕ
hn : 0 < n
⊢ τ f = ↑m / ↑n ↔ ∃ x, (f ^ n) x = x + ↑m

Next tactic:
rw [eq_div_iff, mul_comm, ← translationNumber_pow]
theorem translationNumber_eq_rat_iff (hf : Continuous f) {m : ℤ} {n : ℕ} (hn : 0 < n) :
    τ f = m / n ↔ ∃ x, (f ^ n) x = x + m := by
  rw [eq_div_iff, mul_comm, ← translationNumber_pow] <;> [

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
n : ℕ
hn : 0 < n
⊢ τ (f ^ n) = ↑m ↔ ∃ x, (f ^ n) x = x + ↑m

Next tactic:
skip
theorem translationNumber_eq_rat_iff (hf : Continuous f) {m : ℤ} {n : ℕ} (hn : 0 < n) :
    τ f = m / n ↔ ∃ x, (f ^ n) x = x + m := by
  rw [eq_div_iff, mul_comm, ← translationNumber_pow] <;> [skip; 

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
n : ℕ
hn : 0 < n
⊢ ↑n ≠ 0

Next tactic:
exact ne_of_gt (Nat.cast_pos.2 hn)
theorem translationNumber_eq_rat_iff (hf : Continuous f) {m : ℤ} {n : ℕ} (hn : 0 < n) :
    τ f = m / n ↔ ∃ x, (f ^ n) x = x + m := by
  rw [eq_div_iff, mul_comm, ← translationNumber_pow] <;> [skip; exact ne_of_gt (Nat.cast_pos.2 hn)]
  

Proof state:
f g : CircleDeg1Lift
hf : Continuous ⇑f
m : ℤ
n : ℕ
hn : 0 < n
⊢ τ (f ^ n) = ↑m ↔ ∃ x, (f ^ n) x = x + ↑m

Next tactic:
exact (f ^ n).translationNumber_eq_int_iff (f.continuous_pow hf n)
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  

Proof state:
f g : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
⊢ ∃ F, ∀ (g : G), Semiconj ⇑F ⇑(f₁ g) ⇑(f₂ g)

Next tactic:
have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by rw [h, map_add_one]
      _ ≤ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 :=
        add_le_add_right (map_lt_add_translationNumber_add_one _ _).le _
      _ = x + 2 := by simp [this, add_assoc, one_add_one_eq_two]
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    

Proof state:
f g : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
⊢ ∀ (x : ℝ), BddAbove (range fun g => (f₂ g⁻¹) ((f₁ g) x))

Next tactic:
refine' fun x => ⟨x + 2, _⟩
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    

Proof state:
f g : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
x : ℝ
⊢ x + 2 ∈ upperBounds (range fun g => (f₂ g⁻¹) ((f₁ g) x))

Next tactic:
rintro _ ⟨g, rfl⟩
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    

Proof state:
case intro
f g✝ : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
x : ℝ
g : G
⊢ (fun g => (f₂ g⁻¹) ((f₁ g) x)) g ≤ x + 2

Next tactic:
have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      

Proof state:
f g✝ : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
x : ℝ
g : G
⊢ τ (f₂ g⁻¹) = -τ (f₂ g)

Next tactic:
rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    

Proof state:
case intro
f g✝ : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
x : ℝ
g : G
this : τ (f₂ g⁻¹) = -τ (f₂ g)
⊢ (fun g => (f₂ g⁻¹) ((f₁ g) x)) g ≤ x + 2

Next tactic:
calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by rw [h, map_add_one]
      _ ≤ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 :=
        add_le_add_right (map_lt_add_translationNumber_add_one _ _).le _
      _ = x + 2 := by simp [this, add_assoc, one_add_one_eq_two]
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by 

Proof state:
f g✝ : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
x : ℝ
g : G
this : τ (f₂ g⁻¹) = -τ (f₂ g)
⊢ (f₂ g⁻¹) (x + τ (f₁ g) + 1) = (f₂ g⁻¹) (x + τ (f₂ g)) + 1

Next tactic:
rw [h, map_add_one]
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by rw [h, map_add_one]
      _ ≤ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 :=
        add_le_add_right (map_lt_add_translationNumber_add_one _ _).le _
      _ = x + 2 := by 

Proof state:
f g✝ : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
x : ℝ
g : G
this : τ (f₂ g⁻¹) = -τ (f₂ g)
⊢ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 = x + 2

Next tactic:
simp [this, add_assoc, one_add_one_eq_two]
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by rw [h, map_add_one]
      _ ≤ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 :=
        add_le_add_right (map_lt_add_translationNumber_add_one _ _).le _
      _ = x + 2 := by simp [this, add_assoc, one_add_one_eq_two]
  -- We have a theorem about actions by `OrderIso`, so we introduce auxiliary maps
  -- to `ℝ ≃o ℝ`.
  

Proof state:
f g : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
this : ∀ (x : ℝ), BddAbove (range fun g => (f₂ g⁻¹) ((f₁ g) x))
⊢ ∃ F, ∀ (g : G), Semiconj ⇑F ⇑(f₁ g) ⇑(f₂ g)

Next tactic:
set F₁ := toOrderIso.comp f₁.toHomUnits
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by rw [h, map_add_one]
      _ ≤ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 :=
        add_le_add_right (map_lt_add_translationNumber_add_one _ _).le _
      _ = x + 2 := by simp [this, add_assoc, one_add_one_eq_two]
  -- We have a theorem about actions by `OrderIso`, so we introduce auxiliary maps
  -- to `ℝ ≃o ℝ`.
  set F₁ := toOrderIso.comp f₁.toHomUnits
  

Proof state:
f g : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
this : ∀ (x : ℝ), BddAbove (range fun g => (f₂ g⁻¹) ((f₁ g) x))
F₁ : G →* ℝ ≃o ℝ := MonoidHom.comp toOrderIso (MonoidHom.toHomUnits f₁)
⊢ ∃ F, ∀ (g : G), Semiconj ⇑F ⇑(f₁ g) ⇑(f₂ g)

Next tactic:
set F₂ := toOrderIso.comp f₂.toHomUnits
/-- Consider two actions `f₁ f₂ : G →* CircleDeg1Lift` of a group on the real line by lifts of
orientation preserving circle homeomorphisms. Suppose that for each `g : G` the homeomorphisms
`f₁ g` and `f₂ g` have equal rotation numbers. Then there exists `F : CircleDeg1Lift` such that
`F * f₁ g = f₂ g * F` for all `g : G`.

This is a version of Proposition 5.4 from [Étienne Ghys, Groupes d'homeomorphismes du cercle et
cohomologie bornee][ghys87:groupes]. -/
theorem semiconj_of_group_action_of_forall_translationNumber_eq {G : Type*} [Group G]
    (f₁ f₂ : G →* CircleDeg1Lift) (h : ∀ g, τ (f₁ g) = τ (f₂ g)) :
    ∃ F : CircleDeg1Lift, ∀ g, Semiconj F (f₁ g) (f₂ g) := by
  -- Equality of translation number guarantees that for each `x`
  -- the set `{f₂ g⁻¹ (f₁ g x) | g : G}` is bounded above.
  have : ∀ x, BddAbove (range fun g => f₂ g⁻¹ (f₁ g x)) := by
    refine' fun x => ⟨x + 2, _⟩
    rintro _ ⟨g, rfl⟩
    have : τ (f₂ g⁻¹) = -τ (f₂ g) := by
      rw [← MonoidHom.coe_toHomUnits, MonoidHom.map_inv, translationNumber_units_inv,
        MonoidHom.coe_toHomUnits]
    calc
      f₂ g⁻¹ (f₁ g x) ≤ f₂ g⁻¹ (x + τ (f₁ g) + 1) :=
        mono _ (map_lt_add_translationNumber_add_one _ _).le
      _ = f₂ g⁻¹ (x + τ (f₂ g)) + 1 := by rw [h, map_add_one]
      _ ≤ x + τ (f₂ g) + τ (f₂ g⁻¹) + 1 + 1 :=
        add_le_add_right (map_lt_add_translationNumber_add_one _ _).le _
      _ = x + 2 := by simp [this, add_assoc, one_add_one_eq_two]
  -- We have a theorem about actions by `OrderIso`, so we introduce auxiliary maps
  -- to `ℝ ≃o ℝ`.
  set F₁ := toOrderIso.comp f₁.toHomUnits
  set F₂ := toOrderIso.comp f₂.toHomUnits
  

Proof state:
f g : CircleDeg1Lift
G : Type u_1
inst✝ : Group G
f₁ f₂ : G →* CircleDeg1Lift
h : ∀ (g : G), τ (f₁ g) = τ (f₂ g)
this : ∀ (x : ℝ), BddAbove (range fun g => (f₂ g⁻¹) ((f₁ g) x))
F₁ : G →* ℝ ≃o ℝ := MonoidHom.comp toOrderIso (MonoidHom.toHomUnits f₁)
F₂ : G →* ℝ ≃o ℝ := MonoidHom.comp toOrderIso (MonoidHom.toHomUnits f₂)
⊢ ∃ F, ∀ (g : G), Semiconj ⇑F ⇑(f₁ g) ⇑(f₂ g)

Next tactic:
have hF₁ : ∀ g, ⇑(F₁ g) = f₁ g := fun _ => rfl