function popup(url,a,b) {
	var breedte = a ? a : 350;
	var hoogte = b ? b : 250;
	var boven = Math.floor((top.screen.height - hoogte)/2);
	var links = Math.floor((top.screen.width - breedte)/2);

	var popup = window.open(url,'news','toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=0,copyhistory=0,width='+breedte+',height='+hoogte+',screenX='+links+',screenY='+boven+',left='+links+',top='+boven);
	popup.opener = self;
	popup.focus();
}