rw [Int.ofNat_sub h', Int.ofNat_sub h, Int.ofNat_sub (h.trans_lt h')]
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))
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.succ = ↑(derivative p).natDegree - ↑i + (↑p.natDegree - ↑(derivative p).natDegree.succ)