anchor.diff:      EndKey2 = string:join([key_to_string(Key) || Key <- EndKey1], ", "),
       StartInclusive = lists:keymember(start_inclusive, 1, StartKey1),
       EndInclusive = lists:keymember(end_inclusive, 1, EndKey1),
  -    ColumnTypes = lists:zip(ColNames, ColTypes),
       [Index,
        list_to_binary(Coverage),
        list_to_binary(StartKey2),
        StartInclusive,
        list_to_binary(EndKey2),
        EndInclusive,
  -     list_to_binary(filter_to_string(Filter, ColumnTypes))].
  +     list_to_binary(filter_to_string(Filter, HelperMod))].
   
   %%
   format_coverage(Table, CoverKey, NVal) ->
  
positive.code: explain_sub_query(Index, NVal, ?SQL_SELECT{'FROM' = Table,
                                             'WHERE' = SubQueryWhere,
                                             helper_mod = HelperMod,
                                             partition_key = PartitionKey,
                                             'SELECT' = #riak_sel_clause_v1{
                                                           col_names=ColNames,
                                                           col_return_types=ColTypes}
  
  }) ->
      CoverKey = riak_kv_qry_coverage_plan:make_key(HelperMod, PartitionKey, SubQueryWhere),
      Coverage = format_coverage(Table, CoverKey, NVal),
      {_, StartKey1} = lists:keyfind(startkey, 1, SubQueryWhere),
  
negative.code:         [key_element_to_string(Field), element_to_quoted_string(Value, Type)])).
  
  %%
  -spec filter_to_string([]| {atom(),tuple(),tuple()}, module()) ->
      string().
  filter_to_string([], _Mod) ->
      [];
  filter_to_string({Op, {field,F,_}, {const,V}}, Mod) ->
      Type = Mod:get_field_type([F]),
      lists:flatten(io_lib:format("(~s~s~s)",
                                  [key_element_to_string(F), op_to_string(Op), element_to_quoted_string(V, Type)]));
  filter_to_string({Op, A, B}, Mod) ->
       lists:flatten(io_lib:format("(~s~s~s)",
                                   [filter_to_string(A, Mod), op_to_string(Op), filter_to_string(B, Mod)])).
  
  %%
  op_to_string(and_) -> " AND ";
  