function unternehmen_visible(){
       var e = document.getElementById('u1');
       e.style.visibility = 'visible';
       e = document.getElementById('u2');
       e.style.visibility = 'visible';
       e = document.getElementById('u3');
       e.style.visibility = 'visible';
       e = document.getElementById('u4');
       e.style.visibility = 'visible';              
    }
    function unternehmen_invisible(){
       var e = document.getElementById('u1');
       e.style.visibility = 'hidden';
       e = document.getElementById('u2');
       e.style.visibility = 'hidden';
       e = document.getElementById('u3');
       e.style.visibility = 'hidden';
       e = document.getElementById('u4');
       e.style.visibility = 'hidden';              
    }    
   
    function aktuelles_visible(){
       var e = document.getElementById('a1');
       e.style.visibility = 'visible';
       e = document.getElementById('a2');
       e.style.visibility = 'visible';           
    }
    function aktuelles_invisible(){
       var e = document.getElementById('a1');
       e.style.visibility = 'hidden';
       e = document.getElementById('a2');
       e.style.visibility = 'hidden';           
    }     
   
    function kontakt_visible(){
       var e = document.getElementById('k1');
       e.style.visibility = 'visible';
       e = document.getElementById('k2');
       e.style.visibility = 'visible';   
       e = document.getElementById('k3');
       e.style.visibility = 'visible';                 
    }
    function kontakt_invisible(){
       var e = document.getElementById('k1');
       e.style.visibility = 'hidden';
       e = document.getElementById('k2');
       e.style.visibility = 'hidden';   
       e = document.getElementById('k3');
       e.style.visibility = 'hidden';                  
    }