# Prescribing tangent hyperplanes to $C^{1,1}$ and $C^{1,\omega}$ convex hypersurfaces in Hilbert and superreflexive Banach spaces

## TL;DR

This paper characterizes conditions under which convex hypersurfaces with prescribed tangent hyperplanes exist in Hilbert and superreflexive Banach spaces, extending classical smoothness and convexity results.

## Contribution

It provides necessary and sufficient conditions for constructing $C^{1,1}$ and $C^{1, extomega}$ convex hypersurfaces with given tangent hyperplanes in infinite-dimensional spaces.

## Key findings

- Characterization of tangent hyperplane configurations for $C^{1,1}$ convex hypersurfaces.
- Extension of results to $C^{1, extomega}$ hypersurfaces in Hilbert spaces.
- Application to $C^{1, extalpha}$ hypersurfaces in superreflexive Banach spaces.

## Abstract

Let $X$ denote $\mathbb{R}^n$ or, more generally, a Hilbert space. Given an arbitrary subset $C$ of $X$ and a collection $\mathcal{H}$ of affine hyperplanes of $X$ such that every $H\in\mathcal{H}$ passes through some point $x_{H}\in C$, and $C=\{x_H : H\in\mathcal{H}\}$, what conditions are necessary and sufficient for the existence of a $C^{1,1}$ convex hypersurface $S$ in $X$ such that $H$ is tangent to $S$ at $x_H$ for every $H\in\mathcal{H}$? In this paper we give an answer to this question. We also provide solutions to similar problems for convex hypersurfaces of class $C^{1, \omega}$ in Hilbert spaces, and for convex hypersurfaces of class $C^{1, \alpha}$ in superreflexive Banach spaces having equivalent norms with moduli of smoothness of power type $1+\alpha$, $\alpha\in (0, 1].$