anchor.diff:    outputs = [ "out" "dev" ];
   
     buildInputs = [
  -    (boost.override { enablePython = usePython; })
  -    gmp mpfr libedit python gnused
  +    (boost.override { enablePython = usePython; python = python3; })
  +    gmp mpfr libedit python3 gnused
     ];
   
     nativeBuildInputs = [ cmake texinfo ];
  
positive.code:   # however, that would write to a different nixstore path, pass our own sitePackages location
    prePatch = lib.optionalString usePython ''
      substituteInPlace src/CMakeLists.txt \
        --replace 'DESTINATION ''${Python_SITEARCH}' 'DESTINATION "${python.sitePackages}"'
    '';
  
    installTargets = [ "doc" "install" ];
  
negative.code: { stdenv, lib, fetchFromGitHub, cmake, boost, gmp, mpfr, libedit, python3
  , texinfo, gnused, usePython ? true }:
  
  stdenv.mkDerivation rec {
  