function remove_additional_occurance, a
  h = a
  nel = N_elements(a)
  ri = 1
  for i=1L,nel-1 do begin
     found = 0
     for j=0L,i-1 do begin     
        if a[i] eq a[j] then found = 1
     endfor
     if not found then begin 
        h[ri] = a[i]
        ri += 1
     endif        
  endfor
return, h[0:(ri-1)]
end