anchor.diff:  }:
   
   let
  -  version = "1.6.29";
  +  version = "1.6.30";
   in
   stdenv.mkDerivation rec {
     name = "libpng-${version}";
  
positive.code: 
    patches = [
      (fetchurl {
        url = "mirror://sourceforge/libpng-apng/libpng16/1.6.26/libpng-1.6.26-apng.patch.gz";
        sha256 = "01dec904d91ee8c90a9a78f253d01d8fac0e37a3f4beacb60e136ea7c814d72c";
      })
    ];
  
  
negative.code:   src = fetchurl {
      url = "mirror://sourceforge/libpng/libpng16/${version}/${name}.tar.xz";
      hashOutput = false;
      sha256 = "267c332ffff70cc599d3929207869f698798f1df143aa5f9597b007c14353666";
    };
  
    buildInputs = [
  