perator =&gt;. An AND-LET* form can also be
considered a sequence of guarded expressions. In a regular program,
forms may produce results, bind them to variables and let other forms
use these results. AND-LET* differs in that it checks to make sure that
every produced result "makes sense" (that is, not an #f). The first
"failure" triggers the guard and aborts the rest of the sequence
(which presumably would not make any sense to execute anyway).

Examples:
<PRE>
(AND-LET* ((my-list (compute-list)) ((not (nu