Strictly convex norms and topology

We introduce a new topological property called () and the corresponding class of topological spaces, which includes spaces with $G_\delta$-diagonals and Gruenhage spaces. Using (), we characterise those Banach spaces which admit equivalent strictly convex norms, and give an internal topological characterisation of those scattered compact spaces $K$, for which the dual Banach space $C(K)^$ admits an equivalent strictly convex dual norm. We establish some relationships between () and other topological concepts, and the position of several well-known examples in this context. For instance, we show that $C(\mathcal{K})^$ admits an equivalent strictly convex dual norm, where $\mathcal{K}$ is Kunen’s compact space. Also, under the continuum hypothesis CH, we give an example of a compact scattered non-Gruenhage space having ().