// check browser
var ns4, ie4, ns6;
ns4 = (document.layers)? true:false
ie4 = (document.all)? true:false
ns6 = (document.getElementById)? true:false;

// Show/Hide functions for non-pointer layer/objects
function show_layer(id)
{
    hideAllBut(id);

	if (ns4) {
		document.layers[id].visibility = "show";
	}
	else if (ie4) {
		document.all[id].style.visibility = 'visible';
	}
	else if (ns6) {
		document.getElementById(id).style.visibility= 'visible';
	}
}

function hide_layer(id)
{
	if (ns4) {
		document.layers[id].visibility = "hide";
	}
	else if (ie4) {
		document.all[id].style.visibility = "hidden";
	}
	else if (ns6) {
		document.getElementById(id).style.visibility= 'hidden';
	}
}

function toggle_layer(id)
{
    var isShowing = false;

	if (ns4) {
		isShowing = (document.layers[id].visibility == "hide")?false:true;
	}
	else if (ie4) {
		isShowing = (document.all[id].style.visibility == "hidden")?false:true;
	}
	else if (ns6) {
		isShowing = (document.getElementById(id).style.visibility == 'hidden')?false:true;
	}
	
	if (isShowing) hide_layer(id);
	else           show_layer(id);
}

function hideAllBut(id)
{
 if (id != 'Popup-Programm')          hide_layer('Popup-Programm');
 if (id != 'Popup-Autoren')           hide_layer('Popup-Autoren'); 
 if (id != 'Popup-Unternehmen')       hide_layer('Popup-Unternehmen');
}