  In this paper we consider A-Fredholm and semi-A-Fredholm operators on Hilbert
C*-modules over a W*-algebra A defined in [3],[10]. Using the assumption that A
is a W*-algebra (and not an arbitrary C*-algebra), we obtain several results
such as generalization of Schechter-Lebow characterization of semi-Fredholm
operators and generalization of "punctured neighbourhood" theorem, as well as
some other results that generalize their classical counterparts. We consider
both adjointable and non adjointable semi-Fredholm operators over W*-algebras.
Moreover, we also work with general bounded, adjointable operators with closed
range over C*-algebras and prove a generalization to Hilbert C*-modules of the
result in [1] on Hilbert spaces.
