proposition: Lemma mxtrace_is_scalar : scalar (@mxtrace R n).
proof: Proof. move=> a A B; rewrite mulr_sumr -big_split /=. by apply: eq_bigr=> i _; rewrite !mxE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)