On Shift Dynamics For Cyclically Presented Groups

Abstract

For group presentations with cyclic symmetry, there is a connection between asphericity and the dynamics of the shift automorphism. For the class of groups $G_n(k,l)$ described by the cyclic presentations $\mathcal{P}_n(k,l) = (x_i:x_ix_{i+k}x_{i+l}\ (i \mod n))$ and studied extensively by G. Williams and M. Edjvet \cite{EdjvetWilliams}, the shift acts freely on the nonidentity elements of $G_n(k,l)$ if and only if the presentation $\mathcal{P}_n(k,l)$ is combinatorially aspherical in the sense of \cite{CCH}. The shift has a nonidentity fixed point precisely when $G_n(k,l)$ is finite.