proposition: Lemma pid_mx_minh m n r : pid_mx (minn n r) = pid_mx r :> 'M_(m, n).
proof: Proof. by apply: trmx_inj; rewrite !tr_pid_mx pid_mx_minv. 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)