have h' := natDegree_derivative_lt hp
case neg.a.inr.e_a.e_a
R : Type u_1
inst✝ : CommRing R
p : R[X]
r : R
hp : ¬p.natDegree = 0
i : ℕ
h : i ≤ (derivative p).natDegree
⊢ p.natDegree - (i + 1) = (derivative p).natDegree - i + (p.natDegree - ((derivative p).natDegree + 1))
case neg.a.inr.e_a.e_a
R : Type u_1
inst✝ : CommRing R
p : R[X]
r : R
hp : ¬p.natDegree = 0
i : ℕ
h : i ≤ (derivative p).natDegree
h' : (derivative p).natDegree < p.natDegree
⊢ p.natDegree - (i + 1) = (derivative p).natDegree - i + (p.natDegree - ((derivative p).natDegree + 1))