proposition: Lemma pid_mx_1 r : pid_mx r = 1%:M :> 'M_r.
proof: Proof. by apply/matrixP=> i j; rewrite !mxE ltn_ord andbT. 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)