anchor.diff:    src = fetchurl {
       urls = tarballUrls version;
       hashOutput = false;
  -    sha256 = "25772f653ac5b2e3ceeb89df50e4688891e21f723c460636548971652af0a859";
  +    sha256 = "5ead72b358ec709ed00bbf7a9eaef1654baad937c001c044fe8b74c57f5324e7";
     };
   
     nativeBuildInputs = [
  
positive.code: 
  let
    tarballUrls = version: [
      "mirror://savannah/attr/attr-${version}.src.tar.gz"
    ];
  
    version = "2.4.47";
  in
  stdenv.mkDerivation rec {
    name = "attr-${version}";
  
negative.code:   passthru = {
      srcVerification = fetchurl rec {
        failEarly = true;
        urls = tarballUrls "2.4.48";
        pgpsigUrls = map (n: "${n}.sig") urls;
        pgpKeyFingerprints = [
          "600C D204 FBCE A418 BD2C  A74F 1543 4326 0542 DF34"
          # Mike Frysinger
          "B902 B527 1325 F892 AC25  1AD4 4163 3B9F E837 F581"
        ];
        inherit (src) outputHashAlgo;
        outputHash = "5ead72b358ec709ed00bbf7a9eaef1654baad937c001c044fe8b74c57f5324e7";
      };
    };
  
  