Compact Sparse Merkle Trees (CSMT) [1] is an already existing scheme for shorter proofs, which introduces the new CSMT data structure and was also posted on HN a while ago.[2]
This[3] is the implementation(in Elixir) of the above paper by the author for those interested.
Also, here [4] is an interesting discussion between the author of Compact Sparse Merkle Trees and Vitalik Buterin, the creator of Ethereum on their research forum.
I have posted these links because it seems disingenuous at best and malicious at worst, to not cite this original work which has been extensively discussed and documented before, anywhere in the current paper.
[1] https://eprint.iacr.org/2018/955.pdf [2] https://news.ycombinator.com/item?id=18166298 [3] https://github.com/ZanjeerPlatform/csmt [4] https://ethresear.ch/t/compact-sparse-merkle-trees/3741