In its dynamical formulation, the Furstenberg—Sárközy theorem
states that for any invertible measure-preserving system $(X, \mu,
T)$, any set $A \subseteq X$ with $\mu(A) > 0$, and any integer
polynomial $P$ with $P(0) = 0$,
$$c(A) = \lim_{N-M \to...