var lastCat = null;

function showCat(cat)
{
    var obj = document.getElementById(cat);
    
    if(lastCat==null)
    {
        
        var td = document.getElementById("catParent");
        
        if(td.childNodes.length > 0)
            lastCat = td.childNodes[0];
        else
            return;
    }
    
    lastCat.style.visibility = 'hidden';
    lastCat.style.display = 'none';
    lastCat = obj;
    
    obj.style.visibility = 'visible';
    obj.style.display = 'inline';
 
    
}