Transitive actions of finite abelian groups of sup-norm isometries

There is a long-standing conjecture of Nussbaum which asserts that every finite set in R-n on which a cyclic group of sup-norm isometries acts transitively contains at most 2(n) points. The existing evidence supporting Nussbaum's conjecture only uses abelian properties of the group. It has therefore been suggested that Nussbaum's conjecture might hold more generally for abelian groups of sup-norm isometries. This paper provides evidence supporting this stronger conjecture. Among other results, we show that it, Gamma is an abelian group of sup-norm isometrics that acts transitively on a finite set X in R-n and Gamma contains no anticlockwise additive chains, then X has at most 2(n) points.