(*
    ||M||  This file is part of HELM, an Hypertextual, Electronic        
    ||A||  Library of Mathematics, developed at the Computer Science     
    ||T||  Department, University of Bologna, Italy.                     
    ||I||                                                                
    ||T||  HELM is free software; you can redistribute it and/or         
    ||A||  modify it under the terms of the GNU General Public License   
    \   /  version 2 or (at your option) any later version.              
     \ /   This software is distributed as is, NO WARRANTY.              
      V_______________________________________________________________ *)

type level = int option

(* Interface functions ******************************************************)

let infinite = None

let finite i = Some i

let is_zero xi = 
   xi = (Some 0)

let is_infinite xi =
   xi = None

let succ = function
   | None   -> None
   | Some i -> Some (succ i)

let pred = function
   | None              -> None
   | Some i when i > 0 -> Some (pred i)
   | _                 -> Some 0

let to_string = function
   | None   -> ""
   | Some i -> string_of_int i