Published online by Cambridge University Press: 08 April 2021
We construct an example of a Hamiltonian flow
$f^t$
on a four-dimensional smooth manifold
$\mathcal {M}$
which after being restricted to an energy surface
$\mathcal {M}_e$
demonstrates essential coexistence of regular and chaotic dynamics, that is, there is an open and dense
$f^t$
-invariant subset
$U\subset \mathcal {M}_e$
such that the restriction
$f^t|U$
has non-zero Lyapunov exponents in all directions (except for the direction of the flow) and is a Bernoulli flow while, on the boundary
$\partial U$
, which has positive volume, all Lyapunov exponents of the system are zero.
Dedicated to the memory of Anatole Katok