public function startsWith(Certificate ...$certs): bool
    {
        $n = count($certs);
        if ($n > count($this->_certificates)) {
            return false;
        }
        for ($i = 0; $i < $n; ++$i) {
            if (!$certs[$i]->equals($this->_certificates[$i])) {
                return false;
            }
        }
        return true;
    }