proposition: Lemma exprn_ge0 n x : 0 <= x -> 0 <= x ^+ n.
proof: Proof. by move=> xge0; rewrite -nnegrE rpredX. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)