src/Pure/Thy/present.ML

   | [name, tags] => (name, tags)
   | _ => error ("Malformed document version specification: " ^ quote str));
 
 fun read_versions strs =
   rev (distinct (eq_fst (op =)) (rev ((documentN, "") :: map read_version strs)))
-  |> filter_out (equal "-" o #2);
+  |> filter_out (fn (_, s) => s = "-");
 
 
 (* init session *)
 
 fun name_of_session elems = space_implode "/" ("Isabelle" :: elems);