function nlmenu(posn, artno, last) {
	previous = (artno==1) ? "index.shtml" : ("article" + (artno-1) + ".shtml");
	next = last ? "index.shtml" : ("article" + (artno+1) + ".shtml");
	
	if (posn=="top") {
	    document.write('<a name="Top"></a><center><table>');
	} else {
	    document.write('<center><table><tr><td colspan=3><a href="#Top">Top</a></td></tr>');
	}
	document.write('<tr><td><a href="'
	+ previous +
	'">Previous article</a></td><td><a href="index.shtml">Index</a></td><td><a href="'
	+ next +
	'">Next article</a></td></tr></table></center>');
}