function showLayer(layerName){
		hideAll();
		obj = document.getElementById(layerName);
		obj.style.display = "";
	}
	function hideLayer(layerName){
		obj = document.getElementById(layerName);
		if (obj != null) {
			obj.style.display = "none";
		}
	}
	function hideAll(){
	    for(i = 1; i <= 16; i++) {
			hideLayer('voi' + i);
        }
	}