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. rewrite empstate_empheap in B.
constructor... constructor...
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 lseg_vv sigma v s :
space_denote sigma s =
(space_atom_denote (Lseg (Var v) (Var v)) * space_denote sigma)%pred s.