add contextual subpages

function add_contextual_subpages() {

	if($post->post_parent)
	  	$children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0");
	else
	  	$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
	if ($children) { ?>
		<ul>
		<?php echo $children; ?>
		</ul>
		<?php };


}

add_action('thematic_abovepost', 'add_contextual_subpages')