let pp_ref r fmt p opt_arity=
match opt_arity with
| None ->
Format.fprintf fmt "%s :%a of %d" r pp_root p.p_root
(List.length p.p_off)
| Some ari ->
Format.fprintf fmt "%s :(%a,%d) of %d"
r pp_root p.p_root ari (List.length p.p_off)