General Bourgin-Yang theorems

Abstract

We describe a unified approach to estimating the dimension of $f^{-1}(A)$ for any $G$-equivariant map $f:X\to Y$ and any closed $G$-invariant subset $A\subseteq Y$ in terms of connectivity of $X$ and dimension of $Y$, where $G$ is either a cyclic group of order $p^k$, a $p$-torus ($p$ a prime), or a torus.

Final version. Numerous minor improvements throughout the text to improve readability. 19 pages, no figures