Geometry of Houghton's Groups
  Hougthon's groups H_n is a family of groups where each H_n consists of `translations at infinity' on n rays of discrete points emanating from the origin on the plane. Brown shows H_n has type FP_n-1 but not FP_n by constructing infinite dimensional cell complex on which H_n acts with certain conditions. We modify his idea to construct n-dimensional CAT(0) cubical complex X_n on which H_n acts with the same conditions as before. Brown also shows H_n is finitely presented provided n>2. Johnson provides a finite presentation for H_3. We extend his result to provide finite presentations of H_n for n>3. We also establish exponential isoperimetric inequalities of H_n for n>2. 
Sang Rae Lee
math.GR math.GT