numpy or not numpy?

Description doesn't mention numpy. Sample tests use lists, not numpy arrays. Full tests use numpy. Reference sulution uses numpy, and doesn't pass sample tests!

Is this kata about numpy?

• yes -> numpy should compare somewhere in description or sample tests, we don't have a crystal ball
• no -> numpy should not be used in full tests

I don't understand from the description why is this not 0?

6174 -> 6174

and this not 1?

9999 -> 0000
0000 -> 0000

(Maybe it has something to do with less than 4 digits, but there's padded 4-digit 0288 in the example...)