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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.
I guess if it's solid enough it will always work without any problem, you see you used abs() because some tests returned negative value and some worked perfectly, but in maths it should work for all cases I guess.