The Szlenk index and local l_1-indices

Alspach, Dale; Judd, Robert; Odell, Edward

The Szlenk index and local l_1-indices

Authors

Alspach, Dale

Judd, Robert

Odell, Edward

Description

We introduce two new local l_1-indices of the same type as the Bourgain l_1 index; the l_1^+-index and the l_1^+-weakly null index. We show that the l_1^+-weakly null index of a Banach space X is the same as the Szlenk index of X, provided X does not contain l_1. The l_1^+-weakly null index has the same form as the Bourgain l_1 index: if it is countable it must take values omega^alpha for some alpha<omega_1. The different l_1-indices are closely related and so knowing the Szlenk index of a Banach space helps us calculate its local l_1-index, via the l_1^+-weakly null index. We show that I(C(omega^{omega^alpha}))=omega^{1+alpha+1}.
LaTeX2e, 41 pages, to appear in Positivity