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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.
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Actually, sorting identical items should be fast, so I think it's not sorting that's supposed to be banned, but quadratic solutions.
I didn't notice that there was a Haskell translation removed before:
https://www.codewars.com/kata/find-the-unique-number-1/discuss#59469c2caa3b7379540000a4
Can you add them in a fork?
Approved