anchor.diff:  
       echo ISABELLE_LINE_EDITOR=${rlwrap}/bin/rlwrap >>etc/settings
   
  -    for comp in contrib/jdk* contrib/polyml-* contrib/z3-*; do
  +    for comp in contrib/jdk* contrib/polyml-* contrib/z3-* contrib/verit-*; do
         rm -rf $comp/x86*
       done
       '' + (if ! stdenv.isLinux then "" else ''
  
positive.code:       Z3_VERSION=${z3.version}
        Z3_SOLVER=${z3}/bin/z3
        Z3_INSTALLED=yes
      EOF
  
      cat >contrib/polyml-*/etc/settings <<EOF
  
negative.code: { lib, stdenv, fetchurl, perl, perlPackages, makeWrapper, nettools, java, polyml, z3, veriT, rlwrap, makeDesktopItem }:
  # nettools needed for hostname
  
  stdenv.mkDerivation rec {
    pname = "isabelle";
    version = "2021-1";
  
    dirname = "Isabelle${version}";
  
    src = if stdenv.isDarwin
      then fetchurl {
        url = "https://isabelle.in.tum.de/website-${dirname}/dist/${dirname}_macos.tar.gz";
        sha256 = "0n1ls9vwf0ps1x8zpb7c1xz1wkasgvc34h5bz280hy2z6iqwmwbc";
      }
      else fetchurl {
        url = "https://isabelle.in.tum.de/website-${dirname}/dist/${dirname}_linux.tar.gz";
        sha256 = "0jfaqckhg388jh9b4msrpkv6wrd6xzlw18m0bngbby8k8ywalp9i";
      };
  
    nativeBuildInputs = [ makeWrapper ];
    buildInputs = [ perl polyml z3 veriT ]
               ++ lib.optionals (!stdenv.isDarwin) [ nettools java ];
  
    sourceRoot = dirname;
  