#import "../src/cetz-cd.typ": *

// first, one simple arrow

#cetz-cd( ```
    $...$ ar[r] & $C_n$ ar[r, $d_(n - 1)$] ar[d, $u_n$] & $C_(n - 1)$ ar[r] ar[d, $u_(n - 1)$] & $...$;
    $...$ ar[r] & $D_n$ ar[r, $d_(n - 1)$] & $D_(n - 1)$ ar[r] & $...$;
```)