Projecting Lipschitz functions onto spaces of polynomials

TL;DR

This paper explores whether the space of 2-homogeneous polynomials can be complemented within Lipschitz functions on a Banach space, concluding it cannot for spaces with non-trivial type, extending classical linear results.

Contribution

It proves that the space of 2-homogeneous polynomials is not complemented in Lipschitz functions for Banach spaces with non-trivial type, generalizing known linear space results.

Findings

2-homogeneous polynomial space is not complemented in Lipschitz functions

Extension of classical linear complementability results to polynomial spaces

Applicable to Banach spaces with non-trivial type

Abstract

The Banach space $\mathcal{P}({}^2X)$ of $2$-homogeneous polynomials on the Banach space $X$ can be naturally embedded in the Banach space ${{\rm Lip}_0}(B_X)$ of real-valued Lipschitz functions on $B_X$ that vanish at $0$. We investigate whether $\mathcal{P}({}^2X)$ is a complemented subspace of ${{\rm Lip}_0}(B_X)$. This line of research can be considered as a polynomial counterpart to a classical result by Joram Lindenstrauss, asserting that $\mathcal{P}({}^1X)=X^*$ is complemented in ${{\rm Lip}_0}(B_X)$ for every Banach space $X$. Our main result asserts that $\mathcal{P}({}^2X)$ is not complemented in ${{\rm Lip}_0}(B_X)$ for every Banach space $X$ with non-trivial type.