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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.
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BTreeSet. CheckedI don't know if it's best practice but it's clearly clever :)
If the return type is
i32(and notOption<i32>) then it's not up to us to "fix" the empty value case with a default0value. I mean why0anyway, why not-1or-99?