src/HOL/Tools/Predicate_Compile/core_data.ML

   let
     val intros = map (Thm.prop_of o snd) ((#intros o rep_pred_data) value)
   in
     fold Term.add_const_names intros []
       |> (fn cs =>
-        if member (=) cs @{const_name "HOL.eq"} then
+        if member (op =) cs @{const_name "HOL.eq"} then
           insert (op =) @{const_name Predicate.eq} cs
         else cs)
       |> filter (fn c => (not (c = key)) andalso
         (is_inductive_predicate ctxt c orelse is_registered ctxt c))
   end;