proposition: Lemma coef_comp_poly p q n : (p \Po q)`_n = \sum_(i < size p) p`_i * (q ^+ i)`_n.
proof: Proof. by rewrite comp_polyE coef_sum; apply: eq_bigr => i; rewrite coefZ. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)