The group of self-homotopy equivalences of $A_n^2$-polyhedra

Abstract

Let $X$ be a finite type $A_n^2$-polyhedron, $n\ge 2$. In this paper we study the quotient group $\mathcal{E}(X)/{\mathcal{E}}_{\ast }(X)$, where $\mathcal{E}(X)$ is the group of self-homotopy equivalences of $X$ and ${\mathcal{E}}_{\ast }(X)$ the subgroup of self-homotopy equivalences inducing the identity on the homology groups of $X$. We show that not every group can be realised as $\mathcal{E}(X)$ or $\mathcal{E}(X)/{\mathcal{E}}_{\ast }(X)$ for $X$ an $A_n^2$-polyhedron, $n\ge 3$, and specific results are obtained for $n=2$.

Minor corrections, to appear in Journal of Group Theory