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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
No idea, maybe an error with the highlight library in JavaScript.
why your 'return' is red?
yes, I use to work with functional languages that have not that issue, I guess that cloning the list could be enough for avoiding this issue BUT the problem isn't saying it's going to continue using that list or I've to keep the integrity of that list. Tests are passing and performing something that's not requested only "what if..." could be overengineering as well.
this is bad, because it will sort numbers, and you might have a different "numbers" list after using this function