proposition: Lemma tr_pid_mx m n r : (pid_mx r)^T = pid_mx r :> 'M_(n, m).
proof: Proof. by apply/matrixP=> i j /[!mxE]; case: eqVneq => // ->. 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)