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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.
The first 'd' in italics suggests that it was surrounded by stars which were interpreted as formatting.
So, the formula 10 * d * d actually is:
The series from the example 10, 40, 90, 160, ... gives it away too.