Consult for a Regex question

[duj4]

Hi Sofia,

I happend to find the answer of one of the Regex questions on Hackerrank in this repo(https://github.com/sknsht/HackerRank/blob/master/Python/Regex%20and%20Parsing/Validating%20Credit%20Card%20Numbers/Solution.py), but I got a little confused by your answer, could you please help explain it a little further: how does it work of non look-ahead exp "(?!.*(\d)(-?\1){3})" work?

Thanks in advance.