Definition all_assertions_computable  :=
  forall (Espec: OracleKind) psi tx vx (Q: assert), 
     exists k,  assert_safe Espec psi tx vx k = Q.

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