English
If the natDegree of p is less than n, then aeval x p equals the sum from i = 0 to n−1 of coeff i(p) · x^i.
Русский
Если натуральная степень p меньше n, то aeval x p равно суммации от i = 0 до n−1 коэффициентов p_i · x^i.
LaTeX
$$$p.\natDegree < n \\Rightarrow \, \mathrm{aeval}_x p = \sum_{i=0}^{n-1} p_i \cdot x^i$$$
Lean4
theorem aeval_eq_sum_range' [Algebra R S] {p : R[X]} {n : ℕ} (hn : p.natDegree < n) (x : S) :
aeval x p = ∑ i ∈ Finset.range n, p.coeff i • x ^ i :=
by
simp_rw [Algebra.smul_def]
exact eval₂_eq_sum_range' (algebraMap R S) hn x