;; Consider the following function:

$($define $($mystery x y z$)$

$($string$-$append $($substring x $0$ z$)$

$($substring y z$)$

$($substring y $0$ z$)$

$($substring x z$)))$

;; Describe the value that mystery produces when you apply it to two identical

;; arguments for $\}$x$\backslash$mathrm$\{$ and $\}$y$\backslash$mathrm$\{.$

;; $[$TODO$]$ Prose description as a comment.