-type obj = int * uri * bind (* age, uri, binder, contents *)
+and term = Sort of attrs * int (* attrs, hierarchy index *)
+ | LRef of attrs * int (* attrs, position index *)
+ | GRef of attrs * uri (* attrs, reference *)
+ | Cast of attrs * term * term (* attrs, type, term *)
+ | Appl of attrs * term * term (* attrs, argument, function *)
+ | Bind of attrs * bind * term (* attrs, binder, scope *)