src/Pure/Isar/spec_rules.ML

         class1 = class2 andalso
         eq_list (op aconv) (ts1, ts2) andalso
         eq_list Thm.eq_thm_prop (ths1, ths2))
       (#1 o #2);
   val extend = I;
-  fun merge data = Item_Net.merge data;
+  val merge = Item_Net.merge;
 );
 
 val get = Item_Net.content o Rules.get o Context.Proof;
 val get_global = Item_Net.content o Rules.get o Context.Theory;