A combinatorial construction of almost-ramanujan graphs using the zig-zag product
Avraham Ben-Aroya, Amnon Ta‐Shma · 2008
Reingold, Vadhan and Wigderson [21] introduced the graph zig-zag product. This product combines a large graph and a small graph into one graph, such that the resulting graph inherits its size from the large graph, its degree from the small graph and its spectral gap from both. Using this product they gave the first