Compact Perturbations of Fredholm n-Tuples
Răzvan Gelca · Proceedings of the American Mathematical Society · 1994
LetT be an operator on a Hilbert space.We show that the pair (T,T) can be perturbed to an invertible pair if and only if T is Fredholm of index zero.We also exhibit a large class of Fredholm n-tuples acting on a Banach space which cannot be perturbed by finite rank operators to invertible ones.