Proof with simpl; auto.
induction l... unfold lookC, mergeC, id... if_tac... firstorder.
destruct a. intros [H1 H2]. unfold mergeC.
remember (isEq (expr_cmp (expr_get e1 ((e, e0) :: l))
(expr_get e2 ((e, e0) :: l)))) as b.
destruct b. simpl. intros H3. split; auto.
intros H3. unfold expr_eqs_denote. rewrite listd_cons.
split; auto.
assert (H4 : (e2 === expr_get e2 ((e, e0) :: l)) s).
apply expr_get_sound. simpl. split; auto.
apply var_eq_trans with (y:=e2); auto.
rewrite listd_cons. split.
apply expr_get_sound. simpl. split; auto.
apply expr_rewriteC_sound.
assert (H4 : (e1 === expr_get e1 ((e, e0) :: l)) s).
apply expr_get_sound... split...
apply var_eq_trans with (y:=e1). apply var_eq_sym; auto.
apply var_eq_trans with (y:=e2); auto. apply expr_get_sound.
split; auto.
simpl; split; auto.
Qed.

Lemma cclose_aux_sound l s :
listd clause_denote inter TT l s -> expr_eqs_denote (cclose_aux l) s.