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Abstract.
Let G be the automorphism group of a regular right-angled building X. The
“standard uniform lattice” 
is a canonical graph product of finite groups, which acts
discretely on X with quotient a chamber. We prove that the commensurator of 
is
dense in G. This result was also obtained by Haglund (2008). For our proof, we develop carefully a technique of “unfoldings” of complexes of groups. We use unfoldings to construct a sequence of uniform lattices 
, each commensurable to , and then apply the theory of group actions on complexes of groups to the sequence
. As further applications of unfoldings, we determine exactly when the group G is
nondiscrete, and prove that G acts strongly transitively on X.
Received: 2011-11-30
Revised: 2012-05-17
Published Online: 2012-09-01
Published in Print: 2012-09-01
© 2012 by Walter de Gruyter Berlin Boston
