anchor.diff:  
   %% gen_event callbacks
   -export([init/1, handle_event/2, handle_call/2,
  -	 handle_info/2, terminate/2, code_change/3]).
  +         handle_info/2, terminate/2, code_change/3]).
   
   -record(state, { table :: gb_tree(),
  -	         monitors :: gb_tree() }).
  +                 monitors :: gb_tree() }).
   
   %%====================================================================
   
  
positive.code: 
  %% @private
  handle_info({'DOWN', Ref, process, _Pid, _Reason},
  	    #state { monitors = M, table = T} = S) ->
      {value, IH} = gb_trees:lookup(Ref, M),
      {ok,
       S#state { monitors = gb_trees:delete(Ref, M),
  
negative.code: 
  %% @private
  handle_call({install_callbacks, TorrentPid, IH, CBPropList},
              #state { table = T,
                       monitors = M} = S) ->
      NewT = gb_trees:insert(IH, CBPropList, T),
      MRef = erlang:monitor(process, TorrentPid),
      NewM = gb_trees:insert(MRef, IH, M),
  