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kotlinlang

Hey, can you give your opinion about next two variants:
```
sealed class TransactionPeriod(
   open val interval: Interval,
   open val isMonthly: Boolean
) {
  data class Past(
            override val interval: Interval,
            override val isMonthly: Boolean
    ) : TransactionPeriod(interval, isMonthly)

    data class Current(
            override val interval: Interval,
            override val isMonthly: Boolean
    ) : TransactionPeriod(interval, isMonthly)
}
```