proposition: Lemma intro_unitmx A B : B *m A = 1%:M /\ A *m B = 1%:M -> unitmx A.
proof: Proof. by case=> _ /mulmx1_unit[]. 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)