An extension of a theorem of Nicolaescu on spectral flow and the Maslov index

In this paper we extend a theorem of Nicolaescu on spectral flow and the Maslov index. We do this by studying the manifold of Lagrangian subspaces of a symplectic Hilbert space that are Fredholm with respect to a given Lagrangian . In particular, we consider the neighborhoods in this manifold of Lagrangians which intersect nontrivially.