-- Mathlib/NumberTheory/NumberField/Embeddings.lean
theorem finite_of_norm_le (B : ℝ) : {x : K | IsIntegral ℤ x ∧ ∀ φ : K →+* A, ‖φ x‖ ≤ B}.Finite

Proof state:
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
⊢ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}.Finite

Tactic:
have := bUnion_roots_finite (algebraMap ℤ K) (finrank ℚ K) (finite_Icc (-C : ℤ) C)

Result:
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
this :
  (⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C),
        ↑(map (algebraMap ℤ K) f).roots.toFinset).Finite
⊢ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}.Finite

Proof state:
case refine_2
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
this :
  (⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C),
        ↑(map (algebraMap ℤ K) f).roots.toFinset).Finite
x : K
hx : x ∈ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}
h_map_ℚ_minpoly : minpoly ℚ x = map (algebraMap ℤ ℚ) (minpoly ℤ x)
i : ℕ
⊢ ↑|(minpoly ℤ x).coeff i| = ‖(minpoly ℚ x).coeff i‖

Tactic:
rw [h_map_ℚ_minpoly, coeff_map, eq_intCast, Int.norm_cast_rat, Int.norm_eq_abs, Int.cast_abs]

Result:
no goals

Proof state:
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
this :
  (⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C),
        ↑(map (algebraMap ℤ K) f).roots.toFinset).Finite
x : K
hx : x ∈ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}
⊢ ∃ i,
    ∃ (_ : i.natDegree ≤ finrank ℚ K ∧ ∀ (i_1 : ℕ), i.coeff i_1 ∈ Icc (-↑C) ↑C),
      x ∈ ↑(map (algebraMap ℤ K) i).roots.toFinset

Tactic:
have h_map_ℚ_minpoly := minpoly.isIntegrallyClosed_eq_field_fractions' ℚ hx.1

Result:
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
this :
  (⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C),
        ↑(map (algebraMap ℤ K) f).roots.toFinset).Finite
x : K
hx : x ∈ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}
h_map_ℚ_minpoly : minpoly ℚ x = map (algebraMap ℤ ℚ) (minpoly ℤ x)
⊢ ∃ i,
    ∃ (_ : i.natDegree ≤ finrank ℚ K ∧ ∀ (i_1 : ℕ), i.coeff i_1 ∈ Icc (-↑C) ↑C),
      x ∈ ↑(map (algebraMap ℤ K) i).roots.toFinset

Proof state:
case refine_2
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
this :
  (⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C),
        ↑(map (algebraMap ℤ K) f).roots.toFinset).Finite
x : K
hx : x ∈ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}
h_map_ℚ_minpoly : minpoly ℚ x = map (algebraMap ℤ ℚ) (minpoly ℤ x)
i : ℕ
⊢ ↑|(minpoly ℤ x).coeff i| ≤ ↑↑C

Tactic:
refine (Eq.trans_le ?_ <| coeff_bdd_of_norm_le hx.2 i).trans (Nat.le_ceil _)

Result:
case refine_2
K : Type u_1
inst✝⁴ : Field K
inst✝³ : NumberField K
A : Type u_2
inst✝² : NormedField A
inst✝¹ : IsAlgClosed A
inst✝ : NormedAlgebra ℚ A
B : ℝ
C : ℕ := ⌈(B ⊔ 1) ^ finrank ℚ K * ↑((finrank ℚ K).choose (finrank ℚ K / 2))⌉₊
this :
  (⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C),
        ↑(map (algebraMap ℤ K) f).roots.toFinset).Finite
x : K
hx : x ∈ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}
h_map_ℚ_minpoly : minpoly ℚ x = map (algebraMap ℤ ℚ) (minpoly ℤ x)
i : ℕ
⊢ ↑|(minpoly ℤ x).coeff i| = ‖(minpoly ℚ x).coeff i‖