Definition freeable_blocks: list (block * BinInt.Z * BinInt.Z) -> mpred :=
  fold_right (fun (bb: block*BinInt.Z * BinInt.Z) a => 
                        match bb with (b,lo,hi) => 
                                          sepcon (VALspec_range (hi-lo) Share.top (b,lo)) a
                        end)
                    emp.

Lemma semax_return: forall Delta R ret, semax Espec Delta (fun rho => tc_expropt Delta ret (ret_type Delta) rho && RA_return R (cast_expropt ret (ret_type Delta) rho) rho) (Sreturn ret) R.