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