Proof with simpl; auto.
intros; unfold normalize_atoms; rewrite listd_sort_uniq...
induction l... rewrite <-order_eqv_sound, <-IHl...
Qed.

Lemma list_denote_normalize_filter_nonreflex_atom B l :
list_denote pure_atom_denote inter B
(normalize_atoms (filter nonreflex_atom l)) =
list_denote pure_atom_denote inter B l.