Initial patch. Impl iterator for n-grams

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 14, 2021
LHETILNNYVQ27JCR5WGRAPDRQBFORK77UDJDMAZ4E47PC7ZPS7RAC
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