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 guard_environ_sub:
forall {Delta Delta' f rho},
tycontext_sub Delta Delta' ->
guard_environ Delta' f rho ->
guard_environ Delta f rho.