(* Lemma headptr_field_compatible' {cs: compspecs}: forall t p, headptr p -> legal_alignas_type t = true -> legal_cosu_type t = true -> sizeof t < Ptrofs.modulus -> complete_type cenv_cs t = true -> field_compatible t nil p. *)

Lemma field_at__field_at {cs: compspecs} :
forall sh t gfs v p, v = default_val (nested_field_type t gfs) -> field_at_ sh t gfs p |-- field_at sh t gfs v p.