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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.
I had to submit my solution 3 times - it seems, that author either:
a) found bug in Ruby Prime
b) know better than Ruby Prime if the number is prime or not
What about letting people know how fast is code execution of individual persons katas and giving people score for faster code?
Also what about checking securit issues? (people can audit code of others and check for possible security vulnerabilities and this will result in lowering persons score?)