<script>
    $(function(){
        var a1 = $("#a1");
        var other = $("#a2,#a3,#a4,#a5");
        
        a1.click(function(){
            disabledBox(other,this.checked)
        });
        
        other.click(function() {
              var r = false;
            
            other.each(function() {
                if(this.checked) {
                    r = true;
                    return false;
                  }
            })
              
              disabledBox(a1,r)
        });
       
        //如a1已勾选，则#a2,#a3,#a4,#5锁住
        //disabledBox(other,a1.attr('checked'))
        
        //如#a2,#a3,#a4,#5其中一个或多个已勾选，则a1锁住
        other.each(function() {
             if(this.checked) {
                disabledBox(a1,true)
                 return false;
             }
        })
    });
    
    function disabledBox(el,disabled){
        el.attr("disabled", !!disabled);
    }
</script>