Smooth surjections and surjective restrictions

Abstract

Given a surjective mapping $f:E\to F$ between Banach spaces, we investigate the existence of a subspace $G$ of $E$, with the same density character as $F$, such that the restriction of $f$ to $G$ remains surjective. We obtain a positive answer whenever $f$ is continuous and uniformly open. In the smooth case, we deduce a positive answer when $f$ is a $C^1$-smooth surjection whose set of critical values is countable. Finally we show that, when $f$ takes values in the Euclidean space ${\mathbb{R}}^n$, in order to obtain this result it is not sufficient to assume that the set of critical values of $f$ has zero-measure.

11 pages, a small mistake in the proof of Theorem 8 has been fixed