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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.
Yes, I agree with you, but the spec says: "When provided with a number between 0-9, return it in words." ...... So 10 is not valid input...