def _eval_is_positive(self):
        # Double factorial is positive for every nonnegative input, and for
        # every odd negative input which is of the form -1-4k for an
        # nonnegative integer k
        n = self.args[0]
        if n.is_integer:
            if (n + 1).is_nonnegative:
                return True
            if n.is_odd:
                return ((n + 1) / 2).is_even
dataset/ETHPy150Open sympy/sympy/sympy/functions/combinatorial/factorials.py/factorial2._eval_is_positive/original