Unconditional ideals in Banach spaces
G. Godefroy, N. Kalton, P. Saphar (1993)
Studia Mathematica
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We show that a Banach space with separable dual can be renormed to satisfy hereditarily an “almost” optimal uniform smoothness condition. The optimal condition occurs when the canonical decomposition is unconditional. Motivated by this result, we define a subspace X of a Banach space Y to be an h-ideal (resp. a u-ideal) if there is an hermitian projection P (resp. a projection P with ∥I-2P∥ = 1) on Y* with kernel . We undertake a general study of h-ideals and u-ideals. For example...