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