program nptest
      integer n,i,a
      logical nextp
      external nextp
      parameter(n=4)
      dimension a(n)
      do i=1,n
      a(i)=i
      enddo
   10 print *,(a(i),i=1,n)
      if(nextp(n,a)) go to 10
      end

      function nextp(n,a)
      integer n,a,i,j,k,t
      logical nextp
      dimension a(n)
      i=n-1
   10 if(a(i).lt.a(i+1)) go to 20
      i=i-1
      if(i.eq.0) go to 20
      go to 10
   20 j=i+1
      k=n
   30 t=a(j)
      a(j)=a(k)
      a(k)=t
      j=j+1
      k=k-1
      if(j.lt.k) go to 30
      j=i
      if(j.ne.0) go to 40
      nextp=.false.
      return
   40 j=j+1
      if(a(j).lt.a(i)) go to 40
      t=a(i)
      a(i)=a(j)
      a(j)=t
      nextp=.true.
      end