-- Mathlib/NumberTheory/ClassNumber/AdmissibleCardPowDegree.lean
theorem exists_approx_polynomial_aux [Ring Fq] {d : ℕ} {m : ℕ} (hm : Fintype.card Fq ^ d ≤ m)
    (b : Fq[X]) (A : Fin m.succ → Fq[X]) (hA : ∀ i, degree (A i) < degree b) :
    ∃ i₀ i₁, i₀ ≠ i₁ ∧ degree (A i₁ - A i₀) < ↑(natDegree b - d)

Proof state:
case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj : ¬b.degree ≤ ↑j
⊢ (A i₁).coeff j = (A i₀).coeff j

Tactic:
rw [not_le, degree_eq_natDegree hb] at hbj

Result:
case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj : ↑j < ↑b.natDegree
⊢ (A i₁).coeff j = (A i₀).coeff j

Proof state:
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
A : Fin m.succ → Fq[X]
hA : (A 0).degree < ⊥
⊢ False

Tactic:
exact not_lt_of_le bot_le hA

Result:
no goals

Proof state:
case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj : ↑j < ↑b.natDegree
⊢ (A i₁).coeff j = (A i₀).coeff j

Tactic:
have hbj : j < natDegree b := (@WithBot.coe_lt_coe _ _ _).mp hbj

Result:
case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
⊢ (A i₁).coeff j = (A i₀).coeff j

Proof state:
case pos
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
hd : b.natDegree < d
⊢ b.natDegree - j.succ < d

Tactic:
exact lt_of_le_of_lt tsub_le_self hd

Result:
no goals

Proof state:
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
⊢ b.natDegree - j.succ < d

Tactic:
by_cases hd : natDegree b < d

Result:
case pos
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
hd : b.natDegree < d
⊢ b.natDegree - j.succ < d

case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
hd : ¬b.natDegree < d
⊢ b.natDegree - j.succ < d

Proof state:
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < degree 0
⊢ False

Tactic:
specialize hA 0

Result:
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
A : Fin m.succ → Fq[X]
hA : (A 0).degree < degree 0
⊢ False

Proof state:
case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
hd : ¬b.natDegree < d
⊢ b.natDegree - j.succ < d

Tactic:
rw [not_lt] at hd

Result:
case neg
Fq : Type u_1
inst✝¹ : Fintype Fq
inst✝ : Ring Fq
d m : ℕ
hm : Fintype.card Fq ^ d ≤ m
b : Fq[X]
A : Fin m.succ → Fq[X]
hA : ∀ (i : Fin m.succ), (A i).degree < b.degree
hb : b ≠ 0
f : Fin m.succ → Fin d → Fq := fun i j => (A i).coeff (b.natDegree - ↑j.succ)
this : Fintype.card (Fin d → Fq) < Fintype.card (Fin m.succ)
i₀ i₁ : Fin m.succ
i_ne : i₀ ≠ i₁
i_eq : f i₀ = f i₁
j : ℕ
hj : b.natDegree - d ≤ j
hbj✝ : ↑j < ↑b.natDegree
hbj : j < b.natDegree
hd : d ≤ b.natDegree
⊢ b.natDegree - j.succ < d