proposition: Lemma fullrowsub_free : row_free (rowsub frf A).
proof: Proof. by rewrite row_free_unit fullrowsub_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 finalg zmodp matrix)