proposition: Lemma adj1 n : \adj (1%:M) = 1%:M :> 'M[R]_n.
proof: Proof. by rewrite -{2}(det1 n) -mul_adj_mx mulmx1. 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)