Weekdays are the checkdigit for a date

```dart
bool validateModulus10weight3and1(int target, [int? checkDigit]) => checkDigit == null ? validateModulus10weight3and1(target ~/ 10, target % 10) : (0 <= checkDigit && checkDigit < 10 ? modulus10weight3and1(target) == checkDigit : validateModulus10weight3and1(target ~/ 10, target % 10));
```

É usar um número válido que mas que não exista... Só devem validar o checkdigit

Unfortunately, the algorithm for the check digit on credit cards is not transposition-resistant.

I get the feeling if credit cards were being invented today, it would be.

#transposition #creditcard #checkdigit #errordetection #coding #information