proposition: Lemma sqrtr_ge0 a : 0 <= sqrt a.
proof: Proof. by rewrite /sqrt; case: (sig2W _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)