-- Mathlib/Algebra/Polynomial/SumIteratedDerivative.lean
theorem aeval_sumIDeriv_of_pos [Nontrivial A] [NoZeroDivisors A] (p : R[X]) {q : ℕ} (hq : 0 < q)
    (inj_amap : Function.Injective (algebraMap R A)) :
    ∃ gp : R[X], gp.natDegree ≤ p.natDegree - q ∧
      ∀ (r : A) {p' : A[X]},
        p.map (algebraMap R A) = (X - C r) ^ (q - 1) * p' →
        aeval r (sumIDeriv p) = (q - 1)! • p'.eval r + q ! • aeval r gp

Proof state:
case inr.refine_2.e_a
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
c_le : ∀ (k : ℕ), (c k).natDegree ≤ p.natDegree - k
hc : ∀ (k : ℕ), q ≤ k → ∀ (r : A), (aeval r) ((⇑derivative)^[k] p) = q ! • (aeval r) (c k)
r : A
p' : A[X]
hp : map (algebraMap R A) p = (X - C r) ^ (q - 1) * p'
this✝ : range (p.natDegree + 1) = range q ∪ Ico q (p.natDegree + 1)
this : range q = range (q - 1 + 1)
k : ℕ
hk : k ∈ Ico q (p.natDegree + 1)
⊢ (aeval r) ((⇑derivative)^[k] p) = q ! • (aeval r) (c k)

Tactic:
exact hc k (mem_Ico.mp hk).1 r

Result:
no goals

Proof state:
case right
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : 0 = (X - C r) ^ (q - 1) * p'
⊢ 0 = (q - 1)! • eval r p'

Tactic:
replace hp := (mul_eq_zero.mp hp.symm).resolve_left ?_

Result:
case right.refine_2
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : p' = 0
⊢ 0 = (q - 1)! • eval r p'

case right.refine_1
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : 0 = (X - C r) ^ (q - 1) * p'
⊢ ¬(X - C r) ^ (q - 1) = 0

Proof state:
case right
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : map (algebraMap R A) 0 = (X - C r) ^ (q - 1) * p'
⊢ (aeval r) (sumIDeriv 0) = (q - 1)! • eval r p' + q ! • (aeval r) 0

Tactic:
rw [map_zero, map_zero, smul_zero, add_zero]

Result:
case right
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : map (algebraMap R A) 0 = (X - C r) ^ (q - 1) * p'
⊢ 0 = (q - 1)! • eval r p'

Proof state:
case right
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : map (algebraMap R A) 0 = (X - C r) ^ (q - 1) * p'
⊢ 0 = (q - 1)! • eval r p'

Tactic:
rw [Polynomial.map_zero] at hp

Result:
case right
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
r : A
p' : A[X]
hp : 0 = (X - C r) ^ (q - 1) * p'
⊢ 0 = (q - 1)! • eval r p'

Proof state:
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
k : ℕ
⊢ (if hk : q ≤ k then ⋯.choose else 0).natDegree ≤ p.natDegree - k

Tactic:
split_ifs with h

Result:
case pos
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
k : ℕ
h : q ≤ k
⊢ ⋯.choose.natDegree ≤ p.natDegree - k

case neg
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
k : ℕ
h : ¬q ≤ k
⊢ natDegree 0 ≤ p.natDegree - k

Proof state:
case hq
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
c_le : ∀ (k : ℕ), (c k).natDegree ≤ p.natDegree - k
hc : ∀ (k : ℕ), q ≤ k → ∀ (r : A), (aeval r) ((⇑derivative)^[k] p) = q ! • (aeval r) (c k)
r : A
hp : p = 0
⊢ False

Tactic:
exact p0 hp

Result:
no goals

Proof state:
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
c_le : ∀ (k : ℕ), (c k).natDegree ≤ p.natDegree - k
hc : ∀ (k : ℕ), q ≤ k → ∀ (r : A), (aeval r) ((⇑derivative)^[k] p) = q ! • (aeval r) (c k)
r : A
p' : A[X]
hp : map (algebraMap R A) p = (X - C r) ^ (q - 1) * p'
⊢ q - 1 + p'.natDegree = (map (algebraMap R A) p).natDegree

Tactic:
rw [hp, natDegree_mul, natDegree_pow, natDegree_X_sub_C, mul_one,
  ← Nat.sub_add_comm (Nat.one_le_of_lt hq)]

Result:
case hp
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
c_le : ∀ (k : ℕ), (c k).natDegree ≤ p.natDegree - k
hc : ∀ (k : ℕ), q ≤ k → ∀ (r : A), (aeval r) ((⇑derivative)^[k] p) = q ! • (aeval r) (c k)
r : A
p' : A[X]
hp : map (algebraMap R A) p = (X - C r) ^ (q - 1) * p'
⊢ (X - C r) ^ (q - 1) ≠ 0

case hq
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
c_le : ∀ (k : ℕ), (c k).natDegree ≤ p.natDegree - k
hc : ∀ (k : ℕ), q ≤ k → ∀ (r : A), (aeval r) ((⇑derivative)^[k] p) = q ! • (aeval r) (c k)
r : A
p' : A[X]
hp : map (algebraMap R A) p = (X - C r) ^ (q - 1) * p'
⊢ p' ≠ 0

Proof state:
case neg
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
k : ℕ
h : ¬q ≤ k
⊢ natDegree 0 ≤ p.natDegree - k

Tactic:
rw [natDegree_zero]

Result:
case neg
R : Type u_1
inst✝⁴ : CommSemiring R
A : Type u_3
inst✝³ : CommRing A
inst✝² : Algebra R A
inst✝¹ : Nontrivial A
inst✝ : NoZeroDivisors A
p : R[X]
q : ℕ
hq : 0 < q
inj_amap : Function.Injective ⇑(algebraMap R A)
p0 : p ≠ 0
c : ℕ → R[X] := fun k => if hk : q ≤ k then ⋯.choose else 0
k : ℕ
h : ¬q ≤ k
⊢ 0 ≤ p.natDegree - k