law: 17. Discharge.-
  (1) Every qualified person enlisted under this Act shall be entitled to receive his discharge from national service on the expiration of the period for which he was enlisted and such person may, prior to the expiration of that period, be discharged from national service by such authority and subject to such conditions as may be prescribed.
  (2) A person receiving discharge under this section shall be given a certificate in such form as may be prescribed certifying that he has been discharged from national service.
  (3) A person who has received discharge under this section shall not be required to render national service after such discharge:
  Provided that a person who has received discharge under this section before he has completed four years of national service, shall, unless he has ceased to be liable to be called up for national service under this Act, be liable to be called up for national service under this Act for such term as will, together with the period of national service rendered by him, be equivalent to four years.