anchor.diff:  
   -include("ns_common.hrl").
   
  +%% identifier of ns_vbm_sup childs in supervisors. NOTE: vbuckets
  +%% field is sorted. We could use ordsets::ordset() type, but we also
  +%% want to underline that vbuckets field is never empty.
   -record(new_child_id, {vbuckets::[vbucket_id(), ...],
                          src_node::node()}).
   
  
positive.code:         lists:flatmap(
            fun (Dst) ->
                    Children = try children(Dst, Bucket) catch _:_ -> [] end,
                    [{{Src, Dst}, lists:sort(VBuckets)}
                     || #new_child_id{vbuckets=VBuckets, src_node=Src} <- Children]
            end, RelevantNodes),
      Replicators = dict:from_list(ReplicatorsList),
  
negative.code:                     ?log_info("~p: killed last vbucket (~p) for destination ~p", [SrcNode, VBucket, DstNode]),
                      ok;
                  _ ->
                      {ok, _} = start_child(SrcNode, Bucket,
                                            ordsets:del_element(VBucket, VBuckets),
                                            DstNode)
              end
      end.
  