Let $\mathbb{Q}$ be the D368: Set of rational numbers.
Let $\cdot$ be the D608: Integer multiplication operation.
The rational multiplication operation is the D554: Binary operation
\begin{equation}
\mathbb{Q} \times \mathbb{Q} \to \mathbb{Q}, \quad
[(a, b)] [(c, d)] = [(a c, b d)]
\end{equation}