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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.
Great solution here, but one thing interests me here. Why is the variable
emarked as mutable?entry(x).or_default()already returns a mutable reference.