(** Third, if a struct is a prefix of another, the offsets of common fields are the same. *)

(* Specifications: *)
Lemma field_offset_prefix:
forall env id ofs fld2 fld1,
field_offset env id fld1 = OK ofs ->
field_offset env id (fld1 ++ fld2) = OK ofs.
Lemma field_offset_prefix:
forall env id ofs fld2 fld1,
field_offset env id fld1 = OK ofs ->
field_offset env id (fld1 ++ fld2) = OK ofs.