Multiple correlation sequences not approximable by nilsequences
We show that there is a measure-preserving system (X,B,μ,T) together with functions F0,F1,F2∈L∞(μ) such that the correlation sequence CF0,F1,F2(n)=∫XF0⋅TnF1⋅T2nF2dμ is not an approximate integral combination of 2-step nilsequences.
|Organisation||Algorithms and Complexity|
Briët, J, & Green, B. (2020). Multiple correlation sequences not approximable by nilsequences.