function check_all (bill) {
    
    count = document.bill.elements.length;
	if (document.bill.elements[0].checked == 1) {
    	for (i=0; i < count; i++) {
			document.bill.elements[i].checked = 0;
		}
    } else {
        for (i=0; i < count; i++) {
			document.bill.elements[i].checked = 1;
		}
	}
}