nspl\ds\Set::isSubset PHP Метод

    public function isSubset($sequence)
    {
        if ($sequence instanceof Set) {
            return array_intersect_key($this->array, $sequence->array) === $this->array;
        }
        args\expects(args\traversable, $sequence);
        $size = count($this->array);
        $present = array();
        foreach ($sequence as $element) {
            $elementKey = static::getElementKey($element);
            if (isset($this->array[$elementKey]) || array_key_exists($element, $this->array)) {
                $present[$element] = true;
                if (count($present) === $size) {
                    return true;
                }
            }
        }
        return false;
    }