It's nice because, 


{min(x y)

    ≝ (if {x ≤ y}

         x

        y)

 }


is basically how a mathematician defines a function,

\\[
\begin{align}
\min(x,y)
\overset{\mathrm{def}}{=} \texttt{if } [x \leq y] \\\\
\texttt{then } x ; \\\\
\texttt{else } y. \\\\
\end{align}
\\]