Singular points of order k of Clarke regular and arbitrary functions

Abstrakt

Let $X$ be a separable Banach space and $f$ a locally Lipschitz real function on $X$. Singular points of order $k$ of $f$ are those points at which the Clarke subdifferential of $f$ is at least $k$-dimensional.

We prove that if $f$ is Clarke regu lar, then the set of all singular points of order $k$ of $f$ can be covered by countably many Lipchitz surfaces of codimension $k$. We prove also two results on arbitrary functions, which work with Hadamard directional derivatives and can be considered as generalization of the above result on Clarke regular functions.

Klíčová slova

• Clarke regular functions
• singularities
• Hadamard derivative