src/ZF/Tools/datatype_package.ML

   val case_varname = "f";                (*name for case variables*)
 
   (** Define the constructors **)
 
   (*The empty tuple is 0*)
-  fun mk_tuple [] = @{const "0"}
+  fun mk_tuple [] = @{const zero}
     | mk_tuple args = foldr1 (fn (t1, t2) => Pr.pair $ t1 $ t2) args;
 
   fun mk_inject n k u = Balanced_Tree.access
     {left = fn t => Su.inl $ t, right = fn t => Su.inr $ t, init = u} n k;