private static function checkSeqType($seqTp)
    {
        $seqTp = strtoupper($seqTp);

        if( in_array($seqTp, [self::SEQUENCE_TYPE_FIRST, self::SEQUENCE_TYPE_RECURRING,
                              self::SEQUENCE_TYPE_ONCE, self::SEQUENCE_TYPE_FINAL]) )
            return $seqTp;

        return false;
    }