proposition: Lemma permKV s : cancel s^-1 s.
proof: Proof. by have:= permK s^-1; rewrite invgK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finfun bigop finset binomial) mathcomp(fingroup morphism)