src/HOL/Tools/TFL/rules.ML

 val tracing = ref false;
 
 fun say s = if !tracing then writeln s else ();
 
 fun print_thms s L =
-  say (cat_lines (s :: map string_of_thm L));
+  say (cat_lines (s :: map Display.string_of_thm L));
 
 fun print_cterms s L =
-  say (cat_lines (s :: map string_of_cterm L));
+  say (cat_lines (s :: map Display.string_of_cterm L));
 
 
 (*---------------------------------------------------------------------------
  * General abstraction handlers, should probably go in USyntax.
  *---------------------------------------------------------------------------*)

      let fun cong_prover ss thm =
          let val dummy = say "cong_prover:"
              val cntxt = MetaSimplifier.prems_of_ss ss
              val dummy = print_thms "cntxt:" cntxt
              val dummy = say "cong rule:"
-             val dummy = say (string_of_thm thm)
+             val dummy = say (Display.string_of_thm thm)
              val dummy = thm_ref := (thm :: !thm_ref)
              val dummy = ss_ref := (ss :: !ss_ref)
              (* Unquantified eliminate *)
              fun uq_eliminate (thm,imp,thy) =
                  let val tych = cterm_of thy