anchor.diff:    src = fetchurl {
       url = "mirror://sourceforge/libpng/libpng16/${version}/${name}.tar.xz";
       hashOutput = false;
  -    sha256 = "23912ec8c9584917ed9b09c5023465d71709dce089be503c7867fec68a93bcd7";
  +    sha256 = "eceb924c1fa6b79172fdfd008d335f0e59172a86a66481e09d4089df872aa319";
     };
   
     buildInputs = [
  
positive.code: }:
  
  let
    version = "1.6.35";
  in
  stdenv.mkDerivation rec {
    name = "libpng-${version}";
  
negative.code:   patches = [
      (fetchurl {
        url = "mirror://sourceforge/libpng-apng/libpng16/${version}/${name}-apng.patch.gz";
        sha256 = "8c1f33da739b29a77e35e5a1ebcdffaab63bfe184be8b5a97677cc80156fdc0f";
      })
    ];
  
    passthru = {
      srcVerification = fetchurl {
        failEarly = true;
        inherit (src)
          urls
          outputHash
          outputHashAlgo;
        fullOpts = { };
      };
    };
  
  