proposition: Lemma comm_mxN1 f : comm_mx f (- 1%:M).
proof: Proof. exact/comm_mxN/comm_mx1. 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)