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Journal of Convex Analysis 20 (2013), No. 1, 013--023
Copyright Heldermann Verlag 2013

The One and Half Ball Property in Spaces of Vector-Valued Functions

T. S. S. R. K. Rao
Indian Statistical Institute, R. V. College P.O., Bangalore 560059, India


We exhibit new classes of Banach spaces that have the strong-$1\frac{1}{2}$-ball property and the $1\frac{1}{2}$-ball property by considering direct-sums of Banach spaces. We introduce the notion of sectional strong-$1\frac{1}{2}$-ball property and show that in $c_0$-direct sum of reflexive spaces, proximinal and factor reflexive spaces with the sectional strong-$1\frac{i}{2}$-ball property have the strong-$1\frac{1}{2}$-ball property. We give examples of proximinal hyperplanes in $c_0$ that fail the $1\frac{1}{2}$-ball property and show that this property is in general, not preserved under finite intersections or sums. We show that the range of a bi-contractive projection in $\ell^{\infty}$ has the strong-$1\frac{1}{2}$-ball property. For a separable subspace $Y \subset X$ with the strong-$1\frac{1}{2}$-ball property and for any positive, $\sigma$-finite, non-atomic measure space $(\Omega, {\mathcal A}, \mu)$, we show that $L^1(\mu,Y)$ has the strong-$1\frac{1}{2}$-ball property in $L^1(\mu,X)$. We show that for any compact set $\Omega$ and $Y \subset X$ with the $1\frac{1}{2}$-ball property, $C(\Omega,Y)$ has the $1\frac{1}{2}$-ball property in $C(\Omega,X)$.

Keywords: One and half ball property, spaces of vector-valued functions.

MSC: 41A65,46B20; 41A50

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