Definition all_assertions_computable  :=
forall (Espec: OracleKind) psi tx vx (Q: assert),
exists k,  assert_safe Espec psi tx vx k = Q.
(* This is not generally true, but could be made true by adding an "assert" operator to the programming language *)

Lemma semax_frame {CS: compspecs} {Espec: OracleKind}:  forall Delta P s R F,
closed_wrt_modvars s F ->
semax Espec Delta P s R ->
semax Espec Delta (fun rho => P rho * F rho) s (frame_ret_assert R F).