Let $X_1, \ldots, X_{N + 1}$ each be a D11: Set such that
(i) | $\prod_{n = 1}^{N + 1} X_n$ and $(\prod_{n = 1}^N X_n) \times X_{N + 1}$ are each a D326: Cartesian product |
Then
\begin{equation}
\left| \prod_{n = 1}^{N + 1} X_n \right|
= \left| \left( \prod_{n = 1}^N X_n \right) \times X_{N + 1} \right|
\end{equation}