Definition:Multiplication of Positive Cuts

Definition
Let $0^*$ denote the rational cut associated with the (rational) number $0$.

Let $\alpha$ and $\beta$ be positive cuts, that is, cuts such that $\alpha \ge 0^*$ and $\beta \ge 0^*$, where $\ge$ denotes the ordering on cuts.

Let the operation of multiplication be defined on $\alpha$ and $\beta$ as:
 * $\gamma := \alpha \beta$

where $\gamma$ is the set of all rational numbers $r$ such that either:
 * $r < 0$

or
 * $\exists p \in \alpha, q \in \beta: r = p q$

In this context, $\gamma$ is known as the product of $\alpha$ and $\beta$.

Also see

 * Product of Positive Cuts is Positive Cut which proves existence and uniqueness of $\alpha \beta$