anchor.diff:  
     Boogie = buildDotnetPackage rec {
       baseName = "Boogie";
  -    version = "2019-06-20";
  -    name = "${baseName}-unstable-${version}";
  +    version = "2.4.1";
  +    name = "${baseName}-${version}";
   
       src = fetchFromGitHub {
         owner = "boogie-org";
         repo = "boogie";
  -      rev = "2e8fae4dc1724d8f9e7b1f877116e56b0773337e";
  -      sha256 = "01wjps3yfx8q0qy0zrmmfd1ixjxi2dhkn1wfazb5qm2slav39dp2";
  +      rev = "v${version}";
  +      sha256 = "13f6ifkh6gpy4bvx5zhgwmk3wd5rfxzl9wxwfhcj1c90fdrhwh1b";
       };
   
       # emulate `nuget restore Source/Boogie.sln`
  
positive.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
  
negative.code:     '';
  
      preBuild = ''
        ln -s ${z3} Binaries/z3
      '';
  
      buildInputs = [ Boogie ];
  