proposition: Lemma exprn_even_le0 n x : ~~ odd n -> (x ^+ n <= 0) = (n != 0) && (x == 0).
proof: Proof. by move=> even_n; rewrite real_exprn_even_le0 ?num_real. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)