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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.
what happens when the substring is in the start of the string, i.e what will be the index of the substring in this case?
(hint: only one character has to be added to this line
if s2.find(s1)>0: