“…There are several plausible ways to answer this question, while some basic ideas go back to pioneering works. Among the examples of the recent works, one can refer to [4,5,10,11,13,18] for the non-existence of zero Lyapunov exponents, [9] for uniform hyperbolicity along periodic orbits with one hyperbolic direction and [14] for uniform hyperbolicity along periodic orbits of a shadowable invariant set.…”