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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.
Sorry but your code not working is not a kata issue. Closing.
Using global vars is a source of problems when calling your function multiple times like it's done in the tests. I'm not saying that's the only problem in your code tho.
This comment is hidden because it contains spoiler information about the solution
Got the solucion but tests have a sustract (instead of substract) method