anchor.diff:  
     passthru = {
       inherit version fonts;
  +
  +    srcVerification = fetchurl {
  +      failEarly = true;
  +      md5Url = "${baseUrl}/MD5SUMS";
  +      sha1Url = "${baseUrl}/SHA1SUMS";
  +      sha256Url = "${baseUrl}/SHA256SUMS";
  +      sha512Url = "${baseUrl}/SHA512SUMS";
  +      inherit (src) urls outputHash outputHashAlgo;
  +    };
     };
   
     meta = with stdenv.lib; {
  
positive.code:   inherit (stdenv.lib)
      replaceChars;
  
    version = "9.20";
    versionNoP = replaceChars ["."] [""] version;
  
    fonts = stdenv.mkDerivation {
  
negative.code:     '';
    };
  
    baseUrl = "https://github.com/ArtifexSoftware/ghostpdl-downloads/releases/download/gs${versionNoP}";
  in
  stdenv.mkDerivation rec {
    name = "ghostscript-${version}";
  
    src = fetchurl {
      url = "${baseUrl}/${name}.tar.xz";
      hashOutput = false;
      sha256 = "2be1d014888a34187ad4bbec19ab5692cc943bd1cb14886065aeb43a3393d053";
    };
  
    outputs = [
  