let compare x1 x2 =
match x1, x2 with
| Iof (c1, j1), Iof (c2, j2) ->
let cmp = Pervasives.compare c1 c2 in
if cmp = 0 then Pervasives.compare j1 j2
else cmp
| Size c1, Size c2 -> Pervasives.compare c1 c2
| Iof _, Size _ -> -1
| Size _, Iof _ -> 1