D. Gillet, S. Helou, Y. Rekik, and C. Salzmann. Proceedings of the 1992 ACM conference on Computer-supported cooperative work - CSCW '92, page 107--114. New York, New York, USA, ACM Press, (1992)
C. Neuwirth, D. Kaufer, R. Chandhok, and J. Morris. CSCW '94: Proceedings of the 1994 ACM conference on Computer supported cooperative work, page 145-152. New York, NY, USA, ACM Press, (1994)