proposition: Lemma pid_mx_0 m n : pid_mx 0 = 0 :> 'M_(m, n).
proof: Proof. by apply/matrixP=> i j; rewrite !mxE andbF. 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)