<section>
<title>Recursive Definition</title>
<para>The Fibonacci series begins:
1 1 2 3 5 8 13... Each member of
the series, after the first two,
is the sum of the preceding two
members.</para>
<para>This can be implemented recursively
by calculating the preceding two
members of the series and returning
their sum:</para>
<src:fragment id="sub.fib.recursion">
&fib($n-2) + &fib($n-1);
</src:fragment>
</section>