The aim of this work is to initiate a systematic study of those
properties of Banach space complexes that are stable under certain
perturbations. A Banach space complex is essentially an object of the
form 1 op-l oP +1 ... --+ XP- --+ XP --+ XP --+ ..., where p runs a
finite or infiniteinterval ofintegers, XP are Banach spaces, and oP: Xp
..... Xp+1 are continuous linear operators such that OPOp-1 = 0 for all
indices p. In particular, every continuous linear operator S: X ..... Y,
where X, Yare Banach spaces, may be regarded as a complex: O ..... X Y
..... O. The already existing Fredholm theory for linear operators
suggested the possibility to extend its concepts and methods to the
study of Banach space complexes. The basic stability properties valid
for (semi-) Fredholm operators have their counterparts in the more
general context of Banach space complexes. We have in mind especially
the stability of the index (i.e., the extended Euler characteristic)
under small or compact perturbations, but other related stability
results can also be successfully extended. Banach (or Hilbert) space
complexes have penetrated the functional analysis from at least two
apparently disjoint directions. A first direction is related to the
multivariable spectral theory in the sense of J. L.