intuition.
eapply (rel_map_in H _ _ (VectorDef.to_list a)).
eapply getAllBlists_length_In.
eapply to_list_length.
econstructor.
econstructor.
eauto.
simpl.
rewrite shiftOut_to_list.
econstructor.
eauto.
simpl.
econstructor.
Grab Existential Variables.
intuition.
eapply evalDet_func; eauto.
Qed.

Theorem lowDistApprox_Rnd: forall n2 n1 (a : Bvector n1) r,
lowDistApprox (Rnd n1) a (n1 + n2) r ->
r == (1 / (expnat 2 n1)).