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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.
because output is list
Just like msc3000 said. With more detail; kata itself asks for an array result containing class of each member (data), so in each iteration evaluated adds into the returning array 'Senior' or 'Open' depending on de result of that evaluation. Hope it helps despite my horrible english.
neither me
yes, it's called list comprehension. Without the brackets you will get an error.