Kojiro Taguchi Tomoya Enokido Makoto Takizawa Causality in Hierarchical Group Communication. 568- 2003 conf/icdcsw/2003 ICDCS Workshops http://csdl.computer.org/comp/proceedings/icdcsw/2003/1921/00/19210568abs.htm db/conf/icdcsw/icdcsw2003.html#TaguchiET03