Ltac solve_ptr_derives :=
  repeat rewrite isptr_offset_val;
  apply derives_refl.

Lemma array_at_len_1: forall sh t gfs i v v' p, JMeq v v' -> array_at sh t gfs i (i + 1) (v :: nil) p = field_at sh t (ArraySubsc i :: gfs) v' p.