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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.
He creates a list interpreted as queue which already contains the root node. The queue needs a first element otherwise the while loop would not execute its body.
what does [node] expression mean?