proposition: Lemma addNmx : left_inverse (const_mx 0) oppmx (@addmx V m n).
proof: Proof. by move=> A; apply/matrixP=> i j; rewrite !mxE addNr. 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)