(Cic.term, Cic.lazy_term, Cic.lazy_term GrafiteAst.reduction, string) 
     GrafiteAst.tactic
 
-let singleton = function
+let singleton msg = function
   | [x], _ -> x
-  | _ -> assert false
-;;
+  | l, _   ->
+      let debug = 
+         Printf.sprintf "GrafiteDisambiguate.singleton (%s): %u interpretations"
+        msg (List.length l)
+      in
+      HLog.debug debug; assert false
 
   (** @param term not meaningful when context is given *)
 let disambiguate_term text prefix_len lexicon_status_ref context metasenv term =
   let lexicon_status = !lexicon_status_ref in
   let (diff, metasenv, cic, _) =
-    singleton
+    singleton "first"
       (GrafiteDisambiguator.disambiguate_term ~dbd:(LibraryDb.instance ())
         ~aliases:lexicon_status.LexiconEngine.aliases
         ~universe:(Some lexicon_status.LexiconEngine.multi_aliases)
   (fun context metasenv ugraph ->
     let lexicon_status = !lexicon_status_ref in
     let (diff, metasenv, cic, ugraph) =
-      singleton
+      singleton "second"
         (GrafiteDisambiguator.disambiguate_term ~dbd:(LibraryDb.instance ())
           ~initial_ugraph:ugraph ~aliases:lexicon_status.LexiconEngine.aliases
           ~universe:(Some lexicon_status.LexiconEngine.multi_aliases)
     | CicNotationPt.Inductive _ -> assert false
     | CicNotationPt.Theorem _ -> None in
   let (diff, metasenv, cic, _) =
-    singleton
+    singleton "third"
       (GrafiteDisambiguator.disambiguate_obj ~dbd:(LibraryDb.instance ())
         ~aliases:lexicon_status.LexiconEngine.aliases
         ~universe:(Some lexicon_status.LexiconEngine.multi_aliases) ~uri