src/Pure/term.ML

 fun string_of_vname (x, i) =
   let
     val idx = string_of_int i;
     val dot =
       (case rev (Symbol.explode x) of
-        _ :: "\\<^sub>" :: _ => false
+        _ :: "\<^sub>" :: _ => false
       | c :: _ => Symbol.is_digit c
       | _ => true);
   in
     if dot then "?" ^ x ^ "." ^ idx
     else if i <> 0 then "?" ^ x ^ idx