def close(self):
        if self._subprocess is not None:
            os.killpg(self._subprocess.pid, signal.SIGTERM)
            self._subprocess = None
'in' operator for ProductSets
dataset/ETHPy150Open python-beaver/python-beaver/beaver/ssh_tunnel.py/BeaverSubprocess.close--crossover with--dataset/ETHPy150Open sympy/sympy/sympy/sets/sets.py/ProductSet._contains