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# Introduction

The Luhn algorithm is used to verify card numbers. The algorithm in a summary acts like this:

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, 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!

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