Claims

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1991_03_01_furedi: Theorem 1.4 of Füredi (Combinatorica 1991) bounds the extremal number of the problem's graph H_k by a multiple of n to the three halves for every fixed k, answering Problem 926 affirmatively; refereed and accepted by the site.

2003_11_01_alon_krivelevich_sudakov: Theorem 6.1 of Alon, Krivelevich and Sudakov (Combin. Probab. Comput. 2003) bounds the extremal number of the three-layer Boolean-cube graph H_k on 2n vertices by 4k n^{3/2}, a second proof of Problem 926's answer yes; refereed.

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