Binomial Theorem/Abel's Generalisation/Negative n

Theorem
Abel's Generalisation of Binomial Theorem:

does not hold for $n \in \Z_{< 0}$.

Proof
Putting $n = x = -1$ and $y = z = 1$ into the


 * $\left({-1 + 1}\right)^{-1} = \dfrac 1 0$

which is undefined.

Putting the same values into the gives: