anchor.diff:  
   %%-spec(abort/0::() ->{ok, [filename()]}).
   
  -abort(_IsCompositeRefac) -> %% This function will be extended!
  -    gen_server:call(wrangler_preview_server, abort).
   abort() ->
       gen_server:call(wrangler_preview_server, abort).
      
  
positive.code: -behaviour(gen_server).
  
  %% API
  -export([commit/0, abort/0, abort/1,add_files/1, start_preview_server/0]).
  
  %% gen_server callbacks
  -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  
negative.code: 				  throw(Err1)
       			  end,
       			  case F1==F2 of 
       			      true -> ok; 
       			      false ->
       				  case file:rename(F1, F2) of 
       				      ok -> ok;
  