proposition: Lemma closed_rootP p : reflect (exists x, root p x) (size p != 1).
proof: Proof. exact: PreClosedField.closed_rootP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype bigop finset tuple) mathcomp(div ssralg countalg binomial)