Fixpoint list_drop (A: Type) (n: nat) (l: list A) {struct n} : list A :=
  match n with O => l | S i => match l with nil => nil | _ :: l' => list_drop A i l' end end.Definition straightline (c: Clight.statement) :=
 forall ge ve te k m ve' te' k' m',
        cl_step ge (State ve te (Kseq c :: k)) m (State ve' te' k') m' ->  k=k'.

Lemma extract_exists_pre {CS: compspecs} {Espec: OracleKind}: forall (A : Type) (P : A -> assert) c Delta (R: ret_assert), (forall x, semax Espec Delta (P x) c R) -> semax Espec Delta (fun rho => exp (fun x => P x rho)) c R.