anchor.diff:      '';
   
       preBuild = ''
  -      ln -s ${pkgs.z3} Binaries/z3
  +      ln -s ${z3} Binaries/z3
       '';
   
       buildInputs = [ Boogie ];
  
positive.code: 
    Boogie = buildDotnetPackage rec {
      baseName = "Boogie";
      version = "2019-06-20";
      name = "${baseName}-unstable-${version}";
  
      src = fetchFromGitHub {
        owner = "boogie-org";
        repo = "boogie";
        rev = "2e8fae4dc1724d8f9e7b1f877116e56b0773337e";
        sha256 = "01wjps3yfx8q0qy0zrmmfd1ixjxi2dhkn1wfazb5qm2slav39dp2";
      };
  
      # emulate `nuget restore Source/Boogie.sln`
  
negative.code:     # Boogie as an input is not enough. Boogie libraries need to be at the same
      # place as Dafny ones. Same for "*.dll.mdb". No idea why or how to fix.
      postFixup = ''
        for lib in ${boogie}/lib/dotnet/${boogie.baseName}/*.dll{,.mdb}; do
          ln -s $lib $out/lib/dotnet/${baseName}/
        done
        # We generate our own executable scripts
  