Post History

Cops and Robbers: Luhn algorithm

# Introduction

The [Luhn algorithm](http://enwp.org/Luhn_algorithm) is used to verify card numbers. The algorithm in a summary acts like this:

```lang-none
Reverse the digits, make an array:
    6, 1, 7, 8, 9, 3, 7, 2, 9, 9, 4
Double the numbers in odd indexes:
    6, 2, 7, 16, 9, 6, 7, 4, 9, 18, 4
Sum the digits in each number:
    6, 2, 7, 7, 9, 6, 7, 4, 9, 9, 4
Sum all of the numbers:
    6 + 2 + 7 + 7 + 9 + 6 + 7 + 4 + 9 + 9 + 4 = 70
If the sum modulo 10 is 0, then the number is valid:
    70 % 10 = 0 => valid
```

A challenge of this exists in [CGCC](https://codegolf.stackexchange.com/questions/22/the-luhn-algorithm-for-verifying-credit-card-numbers-etc), but here, let's up the game by playing Cops and Robbers!

# Challenge

Your task as a cop is to write a program in the language of your choice to apply the Luhn algorithm.

- **Input:** Use any form of input for your program, where the supposed variable to be used is either a number or a string.
- **Output:** Print out a value or text that shows if the input is verified by the algorithm. Of course, you have to specify what it exactly is. This helps considering this is a code golfing challenge.
- Use the language of your choice, but make sure that the program abides to having a hidden language used. The more complicated, the better.
- Given this is a code golfing challenge too, make your program as short as possible to make it harder to guess what was used.

If you're a robber, crack the program and figure out which language suffices the program. If you get to do so, post it in the robber's thread and notify the cop.

7 days and if no one guessed the language used, the cop gains a point. The challenge will run until the end of the year (Dec. 31, 2021 23:59 (all timezones)). Most points wins, and bonus points for shortest program!