The images of definable sets in the torus, and their associated Hausdorff limits
For a lattice Λ⊆Rn, let π:Rn→T=Rn/Λ be the projection onto the corresponding torus. In a previous work we considered the closure of π(X) in T, when X is definable in an o minimal structure, and described it in terms of affine real sets, associated to the types on X. The description was uniform in Λ.
We now consider a definable family of sets {Xt:t∈(0,∞)} in Rn, and aim to describe all possible Huasdorff limits in T of π(Xt), as t tends to ∞. We do that (again uniformly in Λ) in terms of affine sets in elementary extensions, associated to types on Xt, for t>>0. Curiously, we conclude that any two such limit sets are, up tp a finite partition, translates of each another.
The problem is a topological analogue, suggested by Amos Nevo, to measure theoretic problems in Ergodic theory, regarding so-called dilations on tori and nilmanifolds.
Joint with Sergei Starchenko.