ode>value</code> is the first value of the set then the special key that holds the first value is returned.
		If <code>value</code> is found in the set, its previous value is returned, otherwise no value is returned.
	</dd>
	
	<dt><code><b>pushback</b>(value)</code></dt>
	<dd>
		Adds <code>value</code> to the end of the set.
		<code>value</code> is returned if successfully added.
		If <code>value</code> is already inserted then the call has no effect and no value is returned.
	</dd>
	
	<dt><code><b>pushfron