Let $x_1, \ldots, x_N \in \mathbb{R}$ and $y_1, \ldots, y_M \in \mathbb{R}$ each be a D993: Real number.

Then \begin{equation} \left( x_1 + \cdots + x_N \right) \left( y_1 + \cdots + y_M \right) = (x_1 y_1 + \cdots + x_1 y_M) + \cdots + (x_N y_1 + \cdots + x_N y_M) \end{equation}