proposition: Lemma det_diag n (d : 'rV[R]_n) : \det (diag_mx d) = \prod_i d 0 i.
proof: Proof. by rewrite det_trig//; apply: eq_bigr => i; 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)