anchor.diff:  
     src = fetchurl {
       url = "https://www.cups.org/software/${version}/cups-${version}-source.tar.bz2";
  -    sha256 = "1gaakz24k6x5nc09rmpiq0xq20j1qdjc3szag8qwmyi4ky6ydmg1";
  +    sha256 = "1bc1y8fjgh54ryh520gk63i5rbagn6jijsrskcqlibhfm0xwmc5s";
     };
   
     buildInputs = [ pkgconfig zlib libjpeg libpng libtiff libusb gnutls libpaper ]
  
positive.code: , libusb ? null, gnutls ? null, avahi ? null, libpaper ? null
  }:
  
  let version = "2.0.4"; in
  
  with stdenv.lib;
  stdenv.mkDerivation {
  
negative.code:       # Work around a Makefile bug.
        "CUPS_PRIMARY_SYSTEM_GROUP=root"
      ];
  
    enableParallelBuilding = true;
  
    postInstall = ''
        # Delete obsolete stuff that conflicts with cups-filters.
  