(1) Institute of Mathematics, Polish Academy of Sciences, Sniadeckich str. 8, Warsaw, Poland;(2) A. Razmadze Mathematical Institute, Georgian Academy of Sciences, M. Aleksidze str. 1, 0193 Tbilisi, Georgia
Abstract:
We discuss Fredholm pairs of subspaces and associated Grassmannians in a Hilbert space. Relations between several existing definitions of Fredholm pairs are established as well as some basic geometric properties of the Kato Grassmannian. It is also shown that the so-called restricted Grassmannian can be endowed with a natural Fredholm structure making it into a Fredholm Hilbert manifold.