let rec find_new_levels(all_ls: level list) (ls: level list) (new_ls: level list): level list =
match ls with
| [] -> new_ls
| hd::tl ->
if (List.mem hd all_ls) then
find_new_levels all_ls tl new_ls
else find_new_levels all_ls tl (new_ls @ [hd])