function showMenu(){
    this.prevObj            = null;
    this.hiddenClassName    = 'hidden'
}

showMenu.prototype.show = function(obj){
    if(this.prevObj!=null){
        $(this.prevObj).addClassName(this.hiddenClassName);
    }
    $(obj).up('ul',0).removeClassName(this.hiddenClassName);
    
    this.prevObj = $(obj).up('ul',0);
}

var showMenu_ = new showMenu();