-- 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:
case refine_1
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)
⊢ (minpoly ℤ x).natDegree ≤ finrank ℚ K

Tactic:
rw [← (minpoly.monic hx.1).natDegree_map (algebraMap ℤ ℚ), ← h_map_ℚ_minpoly]

Result:
case refine_1
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)
⊢ (minpoly ℚ x).natDegree ≤ finrank ℚ K

Proof state:
case refine_1
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)
⊢ (minpoly ℚ x).natDegree ≤ finrank ℚ K

Tactic:
exact minpoly.natDegree_le x

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 | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}.Finite

Tactic:
refine this.subset fun x hx => ?_

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}
⊢ x ∈
    ⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C), ↑(map (algebraMap ℤ K) f).roots.toFinset

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
⊢ {x | IsIntegral ℤ x ∧ ∀ (φ : K →+* A), ‖φ x‖ ≤ B}.Finite

Tactic:
let C := Nat.ceil (max B 1 ^ finrank ℚ K * (finrank ℚ K).choose (finrank ℚ K / 2))

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))⌉₊
⊢ {x | 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))⌉₊
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}
⊢ x ∈
    ⋃ f,
      ⋃ (_ : f.natDegree ≤ finrank ℚ K ∧ ∀ (i : ℕ), f.coeff i ∈ Icc (-↑C) ↑C), ↑(map (algebraMap ℤ K) f).roots.toFinset

Tactic:
simp_rw [mem_iUnion]

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}
⊢ ∃ 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 ∈ Icc (-↑C) ↑C

Tactic:
rw [mem_Icc, ← abs_le, ← @Int.cast_le ℝ]

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| ≤ ↑↑C

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}
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

Tactic:
refine ⟨_, ⟨?_, fun i => ?_⟩, mem_rootSet.2 ⟨minpoly.ne_zero hx.1, minpoly.aeval ℤ x⟩⟩

Result:
case refine_1
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)
⊢ (minpoly ℤ x).natDegree ≤ finrank ℚ K

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 ∈ Icc (-↑C) ↑C