proposition: Lemma root_XaddC a x : root ('X + a%:P) x = (x == - a).
proof: Proof. by rewrite -root_XsubC rmorphN opprK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)