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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 two lines of the pattern matching can be merged into one because at both cases the function returns its argument.
Edit: For this to work, it must be the last line of the function with pattern matching.
How does this work? There isn't an association of Roman numerals with their values.