Theory of Computing
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Title     : On the Elementary Construction of High-Dimensional Expanders by Kaufman and Oppenheim
Authors   : Prahladh Harsha and Ramprasad Saptharishi
Volume    : 20
Number    : 5
Pages     : 1-22
URL       : https://theoryofcomputing.org/articles/v020a005

Abstract
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At STOC 2018, Kaufman and Oppenheim presented an elementary
construction of high-dimensional spectral expanders using elementary
matrices. We give a short, self-contained elementary proof of the
correctness of their construction. As a bonus, this also yields a
simple construction and analysis of standard expanders of bounded
degree.