proposition: Lemma subg_default x : (x \in G) = false -> val (subg x) = 1.
proof: Proof. by move=> Gx; rewrite val_insubd Gx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)