proposition: Lemma diag_mx_is_trig n (r : 'rV[V]_n) : is_trig_mx (diag_mx r).
proof: Proof. exact/is_diag_mx_is_trig/diag_mx_is_diag. 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)