Let $X_1, \ldots, X_N$ each be a D17: Finite set such that

(i)	$K_1, \ldots, K_N \in \mathbb{N}$ are each a D996: Natural number
(ii)	\begin{equation} |X_1| = K_1, \quad \ldots, \quad |X_N| = K_N \end{equation}
(iii)	$X : = X_1 \times \cdots \times X_N$ is the D326: Cartesian product of $X_1, \dots, X_N$
(iv)	$\mathcal{R} : = \{ R : R \subseteq X \}$ is a D5494: Set of N-ary relations on $X$

Then \begin{equation} |\mathcal{R}| = 2^{K_1 K_2 \cdots K_N} \end{equation}