+let rec match_names oi ni os ns =
+ match os, ns with
+ | _ , [] -> None
+ | [] , _ -> None
+ | (_,o)::otl,(_,n)::ntl ->
+ let b = compare_names (snd o) n in
+ if b > 0 then match_names oi (succ ni) os ntl else
+ if b < 0 then match_names (succ oi) ni otl ns else
+ Some (oi, ni)
+