function select_checkboxes(id_prefix,num_start,num_end,select_state) {
	if(num_start > num_end) return;
	var i,checkbox;
	for(i = num_start; i <= num_end; i++)
	{
		checkbox = document.getElementById(id_prefix + i);
		if(checkbox) checkbox.checked = select_state;
	}
}