We present a top-down lower-bound method for depth-4 boolean circuits. In particular, we give
a new proof of the well-known result that the parity function requires depth-4 circuits of size
exponential in n^1/3. Our proof is an application of robust sunflowers and block unpredictability.
Coauthors: Artur Riazanov, Anastasia Sofronova, Dmitry Sokolov

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