ns.
  </p><p>
   Throughout this chapter, it can be useful to look at the reference
   page of the <a class="link" href="sql-createfunction.html" title="CREATE FUNCTION"><code class="command">CREATE
   FUNCTION</code></a> command to
   understand the examples better.  Some examples from this chapter
   can be found in <code class="filename">funcs.sql</code> and
   <code class="filename">funcs.c</code> in the <code class="filename">src/tutorial</code>
   directory in the <span class="productname">PostgreSQL<