Definition bupd_ret_assert (Q: ret_assert): ret_assert :=
          {| RA_normal := fun rho => bupd (RA_normal Q rho);
             RA_break := fun rho => bupd (RA_break Q rho);
             RA_continue := fun rho => bupd (RA_continue Q rho);
             RA_return := fun v rho => bupd (RA_return Q v rho) |}.

Lemma _guard_bupd: forall {Espec: OracleKind} ge Delta (F P: environ -> pred rmap) f k, _guard Espec ge Delta (fun rho => F rho * P rho) f k = _guard Espec ge Delta (fun rho => F rho * bupd (P rho)) f k.