var collimg = new Image(); //preload image
    collimg.src = "img/collapse.gif";
    var expimg = new Image();
    collimg.src = "img/expand.gif";

    
    function ShowHideLayer(boxID)
    {
        /* Obtain reference for the selected boxID layer and its button */
        var box = document.getElementById("box"+boxID);
        var boxbtn = document.getElementById("btn"+boxID);
        
        /* If the selected box is currently invisible, show it */
        if(box.style.display == "none" || box.style.display=="")
            {
            box.style.display = "block";
            boxbtn.src = "img/collapse.gif";
            }
        /* otherwise hide it */
        else
            {
            box.style.display = "none";
            boxbtn.src = "img/expand.gif";
            }
    }
    
    
    /* seconde fonction pour augmenter la taille du div */
    function switchMenu(obj)
    {
        var el = document.getElementById(obj);
        if(el.style.display != "block")
          {
          el.style.display = "block";
          }
        else
          {
          el.style.display = "none"; 
          }
    }