anchor.diff:    src = fetchurl {
       urls = tarballUrls version;
       hashOutput = false;
  -    sha256 = "a8109865f2893f1373b0a8ed5ff7429de8db696fc451b1036bd7bdf95bbeffd6";
  +    sha256 = "87b565e89a9a684fe4ebeeddb8399dce2599f9c9049854ca8c0dfbdea0e21912";
     };
   
     nativeBuildInputs = [
  
positive.code: }:
  
  let
    version = "6.1.1";
  
    tarballUrls = version: [
      "mirror://gnu/gmp/gmp-${version}.tar.bz2"
      "ftp://ftp.gmplib.org/pub/gmp-${version}/gmp-${version}.tar.bz2"
    ];
  in
  stdenv.mkDerivation rec {
  
negative.code:   passthru = {
      srcVerification = fetchurl rec {
        failEarly = true;
        urls = tarballUrls "6.1.2";
        pgpsigUrls = map (n: "${n}.sig") urls;
        pgpKeyFingerprint = "343C 2FF0 FBEE 5EC2 EDBE  F399 F359 9FF8 28C6 7298";
        inherit (src) outputHashAlgo;
        outputHash = "87b565e89a9a684fe4ebeeddb8399dce2599f9c9049854ca8c0dfbdea0e21912";
      };
    };
  
  