English
For all n ∈ ℕ, smeval of X^n · p equals x^n times smeval of p: (X^n · p).smeval x = x^n · p.smeval x.
Русский
Для всех n ∈ ℕ, smeval (X^n · p) = x^n · p.smeval x.
LaTeX
$$$$ (X^n \cdot p).smeval x = x^n \cdot p.smeval x. $$$$
Lean4
theorem smeval_X_mul : (X * p).smeval x = x * p.smeval x := by
induction p using Polynomial.induction_on' with
| add p q ph qh => simp only [smeval_add, ph, qh, mul_add]
| monomial n a =>
rw [← monomial_one_one_eq_X, monomial_mul_monomial, smeval_monomial, one_mul, npow_add, npow_one, ← mul_smul_comm,
smeval_monomial]