intuition.
erewrite groupExp_mod.
simpl.
eapply in_getUnique.
eapply in_flatten.
econstructor.
split.
eapply in_map_iff.
econstructor.
split.
eauto.
eapply filter_In.
split.
eapply in_getUnique.
eapply in_flatten.
econstructor.
split.
eapply in_map_iff.
econstructor.
split.
eapply eq_refl.
eapply in_getAllBvectors.
simpl.
left.
eapply eq_refl.
2:{
rewrite bvToNat_natToBv_inverse.
simpl.
left.
eapply eq_refl.
eapply lognat_monotonic.
eapply modNat_lt.
}
rewrite bvToNat_natToBv_inverse.
unfold ltNatBool.
destruct (lt_dec (modNat k order) order); trivial.
exfalso.
eapply n.
eapply modNat_lt.
eapply lognat_monotonic.
eapply modNat_lt.
apply g_generator.
Qed.

Theorem RndGrpElem_uniform : forall x y,
evalDist RndGrpElem x == evalDist RndGrpElem y.