anchor.diff:  add_to_backups(Files) ->
       gen_server:cast(wrangler_backup_server, {add_backups, Files}).
   
  +%% recover backups for the whole composite refactoring.
   recover_backups() ->
       gen_server:call(wrangler_backup_server, recover_backups).
   
  +%% recover backups for an atomic composite refactoring.
  +rollback_atomic_cr(Pid) ->
  +    gen_server:call(wrangler_backup_server, {rollback_atomic_cr, Pid}).
  +
   reset_backups()->
       gen_server:cast(wrangler_backup_server, reset_backups).
  +
  +add_atomic_cr_start_point(Pid)->
  +    gen_server:cast(wrangler_backup_server, {atomic_cr_starts, Pid}).
   %%====================================================================
   %% gen_server callbacks
   %%====================================================================
  
positive.code: -behaviour(gen_server).
  
  %% API
  -export([start_backup_server/0,add_to_backups/1, recover_backups/0, reset_backups/0]).
  
  %% gen_server callbacks
  -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  
negative.code: -include("../include/wrangler_internal.hrl").
  
  -record(state, {backups=[],
                  preview_pairs=[]}).
  
  %%====================================================================
  