src/HOL/Tools/Sledgehammer/sledgehammer_fact.ML

       map (enclose "[" "]" o Pretty.str_of o Args.pretty_src ctxt) args
       |> implode
 
     fun nth_name j =
       (case xref of
-        Facts.Fact s => backquote s ^ bracket
+        Facts.Fact s => backquote (simplify_spaces (unyxml s)) ^ bracket
       | Facts.Named (("", _), _) => "[" ^ bracket ^ "]"
       | Facts.Named ((name, _), NONE) =>
         make_name reserved (length ths > 1) (j + 1) name ^ bracket
       | Facts.Named ((name, _), SOME intervals) =>
         make_name reserved true