\begin{definition}[Definition:Commensurable]
Let $a, b \in \R_{>0}$ be (strictly) positive real numbers.
$a$ and $b$ are '''commensurable''' {{iff}} $\dfrac a b$ is rational.
{{EuclidSaid}}
:''{{Definition:Euclid's Definitions - Book X/1 - Commensurable}}''
{{EuclidDefRefNocat|X|1|Commensurable}}
\end{definition}