# A Generalized Sharp Whitney Theorem for Jets

### Charles Fefferman

Princeton University, United States

## Abstract

Suppose that, for each point $x$ in a given subset $E \subset \mathbb{R}^n$, we are given an $m$-jet $f(x)$ and a convex, symmetric set $\sigma(x)$ of $m$-jets at $x$. We ask whether there exist a function $F \in C^{m , \omega} ( \mathbb{R}^n )$ and a finite constant $M$, such that the $m$-jet of $F$ at $x$ belongs to $f ( x ) + M \sigma ( x )$ for all $x \in E$. We give a necessary and sufficient condition for the existence of such $F , M$, provided each $\sigma(x)$ satisfies a condition that we call "Whitney $\omega$-convexity''.

## Cite this article

Charles Fefferman, A Generalized Sharp Whitney Theorem for Jets. Rev. Mat. Iberoam. 21 (2005), no. 2, pp. 577–688

DOI 10.4171/RMI/430