-- Mathlib/Algebra/Polynomial/DenomsClearable.lean
theorem one_le_pow_mul_abs_eval_div {K : Type*} [LinearOrderedField K] {f : ℤ[X]} {a b : ℤ}
    (b0 : 0 < b) (fab : eval ((a : K) / b) (f.map (algebraMap ℤ K)) ≠ 0) :
    (1 : K) ≤ (b : K) ^ f.natDegree * |eval ((a : K) / b) (f.map (algebraMap ℤ K))|

Proof state:
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
⊢ b ≠ 0

Tactic:
exact b0.ne.symm

Result:
no goals

Proof state:
case intro.intro.intro
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
ev : ℤ
bi : K
bu : bi * (algebraMap ℤ K) b = 1
hF :
  (algebraMap ℤ K) ev =
    (algebraMap ℤ K) b ^ f.natDegree * eval ((algebraMap ℤ K) a * bi) (Polynomial.map (algebraMap ℤ K) f)
Fa : |↑ev| = ↑b ^ f.natDegree * |eval (↑a * (↑b)⁻¹) (Polynomial.map (algebraMap ℤ K) f)|
⊢ 1 ≤ |ev|

Tactic:
refine Int.le_of_lt_add_one ((lt_add_iff_pos_left 1).mpr (abs_pos.mpr fun F0 => fab ?_))

Result:
case intro.intro.intro
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
ev : ℤ
bi : K
bu : bi * (algebraMap ℤ K) b = 1
hF :
  (algebraMap ℤ K) ev =
    (algebraMap ℤ K) b ^ f.natDegree * eval ((algebraMap ℤ K) a * bi) (Polynomial.map (algebraMap ℤ K) f)
Fa : |↑ev| = ↑b ^ f.natDegree * |eval (↑a * (↑b)⁻¹) (Polynomial.map (algebraMap ℤ K) f)|
F0 : ev = 0
⊢ eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) = 0

Proof state:
case intro.intro.intro
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
ev : ℤ
bi : K
bu : bi * (algebraMap ℤ K) b = 1
hF :
  (algebraMap ℤ K) ev =
    (algebraMap ℤ K) b ^ f.natDegree * eval ((algebraMap ℤ K) a * bi) (Polynomial.map (algebraMap ℤ K) f)
Fa : |↑ev| = ↑b ^ f.natDegree * |eval (↑a * (↑b)⁻¹) (Polynomial.map (algebraMap ℤ K) f)|
⊢ 1 ≤ ↑b ^ f.natDegree * |eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f)|

Tactic:
rw [div_eq_mul_inv, ← Fa, ← Int.cast_abs, ← Int.cast_one, Int.cast_le]

Result:
case intro.intro.intro
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
ev : ℤ
bi : K
bu : bi * (algebraMap ℤ K) b = 1
hF :
  (algebraMap ℤ K) ev =
    (algebraMap ℤ K) b ^ f.natDegree * eval ((algebraMap ℤ K) a * bi) (Polynomial.map (algebraMap ℤ K) f)
Fa : |↑ev| = ↑b ^ f.natDegree * |eval (↑a * (↑b)⁻¹) (Polynomial.map (algebraMap ℤ K) f)|
⊢ 1 ≤ |ev|

Proof state:
case intro.intro.intro.inr
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
ev : ℤ
bi : K
bu : bi * (algebraMap ℤ K) b = 1
Fa : |↑ev| = ↑b ^ f.natDegree * |eval (↑a * (↑b)⁻¹) (Polynomial.map (algebraMap ℤ K) f)|
F0 : ev = 0
hF : eval ((algebraMap ℤ K) a * ((algebraMap ℤ K) b)⁻¹) (Polynomial.map (algebraMap ℤ K) f) = 0
⊢ eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) = 0

Tactic:
rwa [div_eq_mul_inv]

Result:
no goals

Proof state:
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
⊢ ?m.18279 * (algebraMap ℤ K) b = 1

Tactic:
rw [eq_intCast, one_div_mul_cancel]

Result:
K : Type u_1
inst✝ : LinearOrderedField K
f : ℤ[X]
a b : ℤ
b0 : 0 < b
fab : eval (↑a / ↑b) (Polynomial.map (algebraMap ℤ K) f) ≠ 0
⊢ ↑b ≠ 0