Dirichlet to Neumann operator on differential forms

We define the Dirichlet to Neumann operator on exterior dif-ferential forms for a compact Riemannian manifold with boundary and prove that the real additive cohomology structure of the man-ifold is determined by the DN operator. In particular, an explicit formula is obtained which expresses Betti numbers of the manifold through the DN operator. We express also the Hilbert transform through the DN map. The Hilbert transform connects boundary traces of conjugate co-closed forms.