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A Note on Complementary Subspaces in c0

Published online by Cambridge University Press:  20 November 2018

I. D. Berg*
Affiliation:
Queen's University, Kingston, Ontario; University of Illinois, Urbana, Illinois
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A well known result of A. Pelcynski [2] states that each subspace of c0 which is isomorphic to c0 and of infinite deficiency has a complementary subspace which is itself isomorphic to c0. We are concerned here with the question of when there exists R, a subset of the integers, such that the complementary subspace X can actually be taken to be C0(R). That is, we are concerned with determining when the basis vectors for X can be chosen as a subset of the usual basis vectors for c0. If T: C0 → C0 is norm increasing and ‖T‖ < 2, it is not hard to see, as we shall show, that Tco admits a complement of the form C0(R). However, this bound cannot be improved; indeed, it is possible to construct norm increasing T: C0 → C0 such that ‖T‖ = 2 and yet Tc0 admits no such complement. The construction of such a T is the main point of this note. This construction also enables us to dispose of a speculation of ours in [1].

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 1972

References

1. Berg, I. D., Extensions of certain maps to automorphisms of m, Can J. Math. 22 (1970), 308316.Google Scholar
2. Peɫcyński, A., Projections in certain Banach spaces, Studia Math. 19 (1960), 209228.Google Scholar