# A new measure of instability and topological entropy of area-preserving twist diffeomorphisms

```@article{Slijepevi2017ANM,
title={A new measure of instability and topological entropy of area-preserving twist diffeomorphisms},
author={Sini{\vs}a Slijep{\vc}evi{\'c}},
journal={Mathematika},
year={2017},
pages={117-141}
}```
We introduce a new measure of instability of area-preserving twist diffeomorphisms, which generalizes the notions of angle of splitting of separatrices, and flux through a gap of a Cantori. As an example of application, we establish a sharp >0 lower bound on the topological entropy in a neighbourhood of a hyperbolic, unique action-minimizing fixed point, assuming only no topological obstruction to diffusion, i.e. no homotopically non-trivial invariant circle consisting of orbits with the…
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