Proof with simpl; auto; try congruence.
apply prop_ext; split; intro A. destruct (empty_state s) as [s0 [B C]].
exists s0; exists s. split... split... simpl.
constructor... apply empstate_empheap...
apply var_nil_or_loc.
destruct A as [x [y [A [B C]]]]. simpl in B. inversion B; subst...
cut (y = s); [ intro X; rewrite <- X; auto | ].
inversion A; subst. destruct y as [y1 y2], s as [s1 s2]; f_equal...
apply A.
Qed.

(* Specifications: *)
Lemma drop_reflex_lseg_sound sigma s :
space_denote sigma s = space_denote (drop_reflex_lseg sigma) s.