function set_visibility(ids)
{
	var element=document.getElementById(ids);
	element.style.display=(element.style.display)?'':'none';
}

var btm_cur=1;

function btm_next()
{
	if (btm_cur+2<=btm_max)
		btm_cur++;
	var i=0;
	for (i=0; i<=btm_max; i++)
		{
			var e=document.getElementById('btmimg'+i);
			if (i>=btm_cur-1 && i<=btm_cur+1)
				e.style.display='';
			else
				e.style.display='none';
		}
}

function btm_prev()
{
	if (btm_cur-2>=0)
		btm_cur--;
	var i=0;
	for (i=0; i<=btm_max; i++)
		{
			var e=document.getElementById('btmimg'+i);
			if (i>=btm_cur-1 && i<=btm_cur+1)
				e.style.display='';
			else
				e.style.display='none';
		}
}