@classmethod
    def eval(cls, n, k):
        n, k = map(sympify, (n, k))
        d = n - k
        if d.is_zero or k.is_zero:
            return S.One
        elif d.is_zero is False:
            if (1 - k).is_zero:
                return n
            elif k.is_negative:
                return S.Zero
            elif n.is_integer and n.is_nonnegative and d.is_negative:
                return S.Zero
        if k.is_Integer and k > 0 and n.is_Number:
            return cls._eval(n, k)
dataset/ETHPy150Open sympy/sympy/sympy/functions/combinatorial/factorials.py/binomial.eval/swapped operands of `-`