(** Drop an element from a Zlist *)

Fixpoint zdrop (x : Z) (l : Zlist) {struct l} : Zlist :=
  match l with
  | Nil => Nil Z
  | Cons h t => if Zeq_bool x h then t else Cons Z h (zdrop x t)
  end.

Lemma zdrop_head_neq : forall (x y : Z) (l : Zlist), x <> y -> zdrop x (Cons Z y l) = Cons Z y (zdrop x l).