# 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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