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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.
nice solution
well, yes? Or with what logic are you saying that 0 wouldn't be a valid parameter value for this function? It is specified in the kata description that parameter 0 means that there is one square to count the perimeter for - "The function perimeter has for parameter n where n + 1 is the number of squares (they are numbered from 0 to n)"
Does it even need to? (Many edits because i was responding without looking at the problem again)
this solution does not work correctly with $n = 0?