(* 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 data_at_change_composite {cs_from cs_to} {CCE: change_composite_env cs_from cs_to}: forall (sh: Share.t) (t: type) v1 v2,
JMeq v1 v2 ->
cs_preserve_type cs_from cs_to (coeq _ _) t = true ->
@data_at cs_from sh t v1 = @data_at cs_to sh t v2.