## A relation between the topological invariance of the Godbillon-Vey invariant and the Differentiability of Anosov foliations.(English)Zbl 0653.57018

Foliations, Proc. Symp., Tokyo 1983, Adv. Stud. Pure Math. 5, 159-167 (1985).
[For the entire collection see Zbl 0627.00017.]
In this paper, we study Anosov’s unstable foliations of the geodesic flows of negatively curved surfaces to show some relation between the topological invariance of the Godbillon-Vey invariant of codimension one $$C^ 2$$-foliations and the differentiability of such foliations. We treat foliations only on closed oriented 3-manifolds, so that we study the Godbillon-Vey number which is the value of the Godbillon-Vey invariant on the fundamental class of the manifold.

### MSC:

 57R30 Foliations in differential topology; geometric theory 37D99 Dynamical systems with hyperbolic behavior

Zbl 0627.00017