function click_category(id_elem,nb_cat)
 {
    var item = document.getElementById('category_'+id_elem);
    var open = Boolean;
    if(item.style.display=='none')
    	{open=true;}
    else
    	{open=false;}	

    for (i=0; i<nb_cat; i++)
     {
    		document.getElementById('category_'+i).style.display='none'; 		
			}

		if(open)   
    	{	item.style.display='';
    		}
}