wol-soft/php-json-schema-model-generator

is_array($value) && (static function (array $items): bool {
    if (empty($items)) {
        return false;
    }

    asort($items);
    $lastSeen = array_shift($items);

    foreach ($items as $value) {
        if ($value === $lastSeen) {
            return true;
        }

        $lastSeen = $value;
    }

    return false;
})($value)