type r_rel = (position * depth)
type r_sort = (position * depth * sort)
-(*
-type r_obj = (string * string * int option)
-type r_rel = (string * int)
-type r_sort = (string * int * string)
-*)
-
type must_restrictions = (r_obj list * r_rel list * r_sort list)
type only_restrictions =
(r_obj list option * r_rel list option * r_sort list option)