proposition: Lemma mxtrace_diag D : \tr (diag_mx D) = \sum_j D 0 j.
proof: Proof. by apply: eq_bigr => j _; rewrite mxE eqxx. 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)