On the Baire class of $n$-dimensional boundary functions

Abstract

We show an extention of a theorem of Kaczynski to boundary functions in n-dimensional space. Let $H$ denote the upper half-plane, and let $X$ denote its frontier, the $x$-axis. Suppose that $f$ is a function mapping $H$ into some metric space $Y$. If $E$ is any subset of $X$, we will say that a function $\varphi: E \rightarrow Y$ is a boundary function for $f$ if and only if for each $x\in E$ there exists an arc $\gamma$ at $x$ such that $\lim_{z\rightarrow x \atop z\in\gamma} f(z) = \varphi(x)$.