anchor.diff:  findIndex(Pred, Seq) ->
       case find_internal(seq(Seq), Pred) of
           undefined ->
  -            throw(key_not_found_exception);
  +            throw_key_not_found_exn();
           {Index, _Item} ->
               Index
       end.
  
positive.code:                 false ->
                      find_internal0(Enum, Index+1, F)
              end
      end.
  
  aggregate(Enum0, State, F) ->
  
negative.code:         case next(seq(Seq)) of
              finished ->
                  % no items in sequence
                  throw_arg_exn();
              {Item, Enum} ->
                  aggregate(Enum, {1, F(Item)}, Aggr)
          end,
  