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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.
Unfortunately the test cases do not match the description. There shouldn't be any negative input values at all.
That said, it seems, that with the current (haskell) tests it is expected to treat negative values like any other value. Zero is only expected if one of the inputs is zero.
I think this kata needs better tests and a more precise description.