proposition: Lemma val_unitV x : val (x^-1 : unit_of)%g = (val x)^-1.
proof: Proof. by []. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype finset fingroup morphism perm action) mathcomp(ssralg countalg)