Currently Ethereum uses modified Merkle patricia trie and maybe plan to move to a sparse Merkle tree (SMT), which both support `proof of non-inclusion', i.e. allowing one to proof that some key does not stored in the data structure. Simple Merkle trees lack that feature. My question is why is this feature needed in Ethereum?


In some variations of plasma you need to prove that you didn't spend your balance.

For example if you want to exit a instance of plasma.


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