proposition: Lemma mxtraceZ a (A : 'M_n) : \tr (a *: A) = a * \tr A.
proof: Proof. exact: scalarZ. 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)