proposition: Lemma row_free_unit n (A : 'M_n) : row_free A = (A \in unitmx).
proof: Proof. apply/row_fullP/idP=> [[A'] | uA]; first by case/mulmx1_unit. by exists (invmx A); rewrite mulVmx. 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 finalg zmodp matrix)