<expression arity="2" operator="*">
<operand>
<variable>num</variable>
</operand>
<operand>
<call function="factorial">
<argument>
<expression arity="2" operator="-">
<operand>
<variable>num</variable>
</operand>
<operand>
<number>1</number>
</operand>
</expression>
</argument>
</call>