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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.
Well, the kata description says 'The string has a length greater or equal to one and contains only letters from a-z'?
This solution is incorrect. It could be that the test cases provided are not good, but (for example) capital letters are not shown as an error as they should be. Or anything less than 'a' for that matter.