anchor.diff:  , buildPythonPackage
   , fetchPypi
   , isl
  -, pytest
  +, pybind11
  +, pytestCheckHook
  +, pythonOlder
   , cffi
   , six
   }:
  
positive.code:       --replace "\"pytest>=2\"," ""
    '';
  
    buildInputs = [ isl ];
    checkInputs = [ pytest ];
    propagatedBuildInputs = [
      cffi
      six
    ];
  
    checkPhase = ''
      pytest test
    '';
  
    meta = with lib; {
      description = "Python wrapper around isl, an integer set library";
  
negative.code: buildPythonPackage rec {
    pname = "islpy";
    version = "2020.2";
    disabled = pythonOlder "3.6";
  
    src = fetchPypi {
      inherit pname version;
  