gistfile1.h

/*
 * As backward only points to a non-header node,
 * it would be possible to replace the ternary statement with
 * simply "x->backwards", because the condition will always be false.
 *
 * ...right?
 */

static void zslInsert(zskiplist *zsl, double score, robj *obj) {
    ...
    x->backward = (update[0] == zsl->header) ? NULL : update[0];
    ...
}

static int zslDelete(zskiplist *zsl, double score, robj *obj) {
    ....
        if (x->forward[0]) {
            x->forward[0]->backward = (x->backward == zsl->header) ?
                                        NULL : x->backward;
        } else {
            zsl->tail = x->backward;
        }
    ....
}