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It is often important to determine if a list is empty.  This can be done
in many ways, but only two are worth mentioning.  If either the
lh_TailPred field is pointing to the list header or the ln_Succ field of
the lh_Head is NULL, then the list is empty.

In C, for example, these methods would be written as follows:

    /* You can use this method...   */
    if (list->lh_TailPred == (struct Node *)list)
        printf("list is empty\n");

    /* Or you can use this method   */
    if (NULL == list->lh_Head->ln_Succ)
        printf("list is empty\n");

In assembly code, if A0 points to the list header, these methods would be
written as follows:

    ; Use this method...
    BEQ     list_is_empty

    ; Or use this method
    MOVE.L  LH_HEAD(A0),A1
    TST.L   LN_SUCC(A1)
    BEQ     list_is_empty

Because LH_HEAD and LN_SUCC are both zero offsets, the second case may be
simplified or optimized by your assembler.

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