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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.
While slower than the closed form, it certainly is more evocative of the actual problem description. And if it were written in 'math' (Capital Sigma notation), this would be defintion of the problem. Nice.