public byte[] keys() {
	int length = 0;
	Cons c = head;
	while (c != null) {
	    length++;
	    c = c.next;
	}
	byte[] result = new byte[length];
	c = head;
	int j = 0;
	while (c != null) {
	    result[j] = c.b;
	    j++;
	    c = c.next;
	}
	return result;
    }