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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 description is wrong compared to the solutions it's asking for. It's asking you to return the longest string out of 2 but actually it wants you to return all unique characters from BOTH strings.
this is what I was trying to do with my solution, was trying to figure out how to pass a variable to inner function, which in this case is to return a function that takes a variable. Didn't think of that... thank you.