anchor.diff:  
   with lib;
   
  -{
  +let cfg = config.programs.file-roller;
  +
  +in {
   
     # Added 2019-08-09
     imports = [
  
positive.code: 
        enable = mkEnableOption "File Roller, an archive manager for GNOME";
  
      };
  
    };
  
negative.code: 
    ###### implementation
  
    config = mkIf cfg.enable {
  
      environment.systemPackages = [ cfg.package ];
  
      services.dbus.packages = [ cfg.package ];
  
    };
  
  