Proof with auto.
unfold flt.
intros.
intro.
destruct (proj1_conj (filter_In _ _ _) H). clear H.
simpl in H0.
simpl in H2.
destruct (Ecmp ee (subscript k) (subscript (vec.nth v pi))); destruct dr; auto; simpl in H2; try discriminate...
Qed.

Lemma ndi_flt: forall x0 cr, NoDup (flt x0 cr).
Hint Immediate ndi_flt.