function void normalize_list (matrix *x)
  # If the matrix (representing a list) contains var 0,
  # but not in first position, move it to first position
  if (x[1] != 0)
     scalar k = cols(x)
     loop for (i=2; i<=k; i++)
        if (x[i] == 0)
            x[i] = x[1]
            x[1] = 0
            break
         endif
     endloop
  endif
end function

open data9-7
list Xl = 2 3 0 4
matrix x = Xl
normalize_list(&x)
list Xl = x
list Xl print