proposition: Lemma exprz_inv x n : (x^-1) ^ n = x ^ (- n).
proof: Proof. by case: (intP n)=> // m; rewrite -[_ ^ (- _)]exprVn ?opprK ?invrK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(fintype finfun bigop order ssralg countalg ssrnum) mathcomp(poly)