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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.
That sounds like a question, not a kata issue. Also, you should use appropriate formatting. Read this: https://docs.codewars.com/training/troubleshooting#post-discourse
Answering your question, it comes from
b = 'yestheyarehere'.from your test where does 'b' come from?
from Sample Tests we have:
a = aretheyhere, b = yestheyarehere,and result will be "aehrsty"
so... in aehrsty we have "s" letter. where does it come from?