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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.
This is not readily apparent from the description, but you DO NOT have to return the original array, a. You can instead return a NEW array. Makes possible solutions much simpler.