Return NaN instead of Inf from `rising_factorial(n,k)` and `falling_factorial(n,k)` when the denominator is zero (with k < 0)
Return NaN instead of Inf from `rising_factorial(n,k)` and `falling_factorial(n,k)` when the denominator is zero (with k < 0)
trizen/sidef,trizen/sidef,trizen/sidef,trizen/sidef