function open_nav(nummer) {
  if(document.getElementById("bg"+nummer).style.display=="inline") {
    	document.getElementById("bg"+nummer).style.display="none";
			document.getElementById("b"+nummer).src="./images/navigation/buttons/nav_button"+nummer+".jpg";
			document.getElementById("space").style.paddingBottom="20px";
			}
      else {
       document.getElementById("bg"+nummer).style.display="inline";
				document.getElementById("b"+nummer).src="./images/navigation/buttons/nav_hover_button"+nummer+".jpg";
				new_space=parseInt(document.getElementById('space').style.paddingBottom)+130;
				document.getElementById("space").style.paddingBottom=new_space+"px";
			}
     return false;
}