Martin R. Bridson

There is only one gap in the isoperimetric spectrum

Abstract. The closure of the set of isoperimetric exponents for finitely presented groups is

On the existence of flat planes in spaces of nonpositive curvature

\{1\} \cup [2,\infty

On the semisimplicity of polyhedral isometries

. For each pair of positive integers

Structure and finiteness properties of subdirect products of groups

p \ge q

The Subgroups of Direct Products of Surface Groups

, one can construct groups with aspherical presentations for which the Dehn function is

Formal language theory and the geometry of 3-manifolds

\simeq n^{2\alpha}

On the finite presentation of subdirect products and the nature of residually free groups

, where

Homomorphisms from automorphism groups of free groups

\alpha\,=\{\rm log}_{2}(2p/q)

Context-Free Languages of Sub-exponential Growth

.

Combings of semidirect products and 3-manifold groups

Let X be a proper 1-connected geodesic metric space which is non- positively curved in the sense that it satisfies Gromovs CAT(0) condition glob- ally. If X is cocompact, then either it is 6-hyperbolic, for some 6 > 0, or else it contains an isometrically embedded copy of the Euclidean plane; these conditions are mutually exclusive. It follows that if the fundamental group of a compact non-positively curved polyhedron K is not word-hyperbolic, then the universal cover of K contains a flat plane.