Open Access  Subscription Access

The purpose of this paper is to study certain geometrical properties for non-complete normed spaces. We show the existence of a non-rotund Banach space with a rotund dense maximal subspace. As a consequence, we prove that every separable  Banach space can be renormed to be non-rotund and to contain a dense maximal  rotund subspace. We then construct a non-smooth Banach space with a dense maximal smooth subspace. We also study the Krein-Milman property on noncomplete normed spaces and provide a sufficient condition for an infinite dimensional Banach space to have an infinite dimensional, separable quotient.

Keywords: Rotund, smooth, Markushevich basis, dense maximal subspace, cs-closed

Quaestiones Mathematicae 34(2011), 489–511