unfold offset_in_range; intros.
destruct d; simpl in *; trivial.
split; try omega.
apply Z.add_nonneg_nonneg. apply (Ptrofs.unsigned_range i). omega.
Qed.

Lemma sizeof_Zlength_nonneg {A} {ge: composite_env} t (d:list A): 0 <= sizeof t * Zlength d.
specialize (Zlength_nonneg d). specialize (sizeof_pos t); intros.