Let $X \in \text{Random} \{ x_1, \ldots, x_N \}$ and $Y \in \text{Random} \{ y_1, \ldots, y_M \}$ each be a D5723: Simple random variable.
Let $n \in 1, \ldots, N$ be a D5094: Positive integer.

Then \begin{equation} \mathbb{P}(X = x_n) = \sum_{m = 1}^M \mathbb{P}(X = x_n, Y = y_m) \end{equation}