In its dynamical formulation, the Furstenberg—Sárközy theorem
states that for any invertible measure-preserving system (X,μ,T),
any set A⊆X with μ(A) greater than 0, and any integer polynomial P
with P(0)=0,
c(A)=limN−M→∞1N−M∑n=MN−1μ(A∩TP(n)A)>0.
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