proposition: Lemma actrK x : cancel (actr^~ x) (actr^~ x^-1%g).
proof: Proof. move=> u; apply: val_inj; rewrite !fmvalJcond groupV. by case: ifP => -> //; rewrite conjgK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div choice fintype bigop ssralg finset fingroup) mathcomp(morphism perm finalg action gproduct commutator) mathcomp(cyclic)