The author has retracted this article , since a critical error was found in the proof of the main result after its publication, thus making it invalid. The article  was written as a note to a paper by N. Alon and M. Capalbo .
The author is grateful to Professor A. Yavuz Oruҫ (Department of Electrical and Computer Engineering, University of Maryland, College Park, MD) for pointing to the fallacy in the original article.
Bassalygo, L.A., Note on “Smaller Explicit Superconcentrators” by N. Alon and M. Capalbo, Probl. Peredachi Inf., 2019, vol. 55, no. 3, pp. 106–108. https://doi.org/10.1134/S0032946019030086
Alon, N. and Capalbo, M., Smaller Explicit Superconcentrators, Internet Math., 2004, vol. 1, no. 2, pp. 151–163. https://projecteuclid.org/euclid.im/1089229505
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Bassalygo, L. Retraction Note: Note on “Smaller Explicit Superconcentrators” by N. Alon and M. Capalbo. Probl Inf Transm 56, 399 (2020). https://doi.org/10.1134/S0032946020040092