proposition: Lemma deg2_poly_factor : 0 <= delta -> p = ('X - r1%:P) * ('X - r2%:P).
proof: Proof. by move=> dge0; apply: deg2_poly_factor; rewrite ?sqr_sqrtr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)