proposition: Lemma poly2_root p : size p = 2 -> {r | root p r}.
proof: Proof. case: p => [[|p0 [|p1 []]] //= nz_p1]; exists (- p0 / p1). by rewrite /root addr_eq0 /= mul0r add0r mulrC divfK ?opprK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)