let position to_skip n (shift, lc) =
match lc with
- | NCic.Irl _ when to_skip > 0 -> assert false (* unclear to me *)
- | NCic.Irl len when n <= shift || n > shift + len ->
+ | NCic.Irl len when n <= shift + to_skip || n > shift + len ->
raise (NotFound `NotInTheList)
| NCic.Irl _ -> n - shift
| NCic.Ctx tl ->